Chapter 12. Functions and Operators

Table of Contents

12.1. Operators
12.1.1. Operator Precedence
12.1.2. Parentheses
12.1.3. Comparison Functions and Operators
12.1.4. Logical Operators
12.2. Control Flow Functions
12.3. String Functions
12.3.1. String Comparison Functions
12.4. Numeric Functions
12.4.1. Arithmetic Operators
12.4.2. Mathematical Functions
12.5. Date and Time Functions
12.6. What Calendar Is Used By MySQL?
12.7. Full-Text Search Functions
12.7.1. Boolean Full-Text Searches
12.7.2. Full-Text Searches with Query Expansion
12.7.3. Full-Text Stopwords
12.7.4. Full-Text Restrictions
12.7.5. Fine-Tuning MySQL Full-Text Search
12.8. Cast Functions and Operators
12.9. Other Functions
12.9.1. Bit Functions
12.9.2. Encryption Functions
12.9.3. Information Functions
12.9.4. Miscellaneous Functions
12.10. Functions and Modifiers for Use with GROUP BY Clauses
12.10.1. GROUP BY (Aggregate) Functions
12.10.2. GROUP BY Modifiers
12.10.3. GROUP BY with Hidden Fields

Expressions can be used at several points in SQL statements, such as in the ORDER BY or HAVING clauses of SELECT statements, in the WHERE clause of a SELECT, DELETE, or UPDATE statement, or in SET statements. Expressions can be written using literal values, column values, NULL, functions, and operators. This chapter describes the functions and operators that are allowed for writing expressions in MySQL.

An expression that contains NULL always produces a NULL value unless otherwise indicated in the documentation for a particular function or operator.

Note: By default, there must be no whitespace between a function name and the parenthesis following it. This helps the MySQL parser distinguish between function calls and references to tables or columns that happen to have the same name as a function. However, spaces around function arguments are permitted.

You can tell the MySQL server to accept spaces after function names by starting it with the --sql-mode=IGNORE_SPACE option. Individual client programs can request this behavior by using the CLIENT_IGNORE_SPACE option for mysql_real_connect(). In either case, all function names become reserved words. See Section 5.3.2, “The Server SQL Mode”.

For the sake of brevity, most examples in this chapter display the output from the mysql program in abbreviated form. Instead of showing examples in this format:

mysql> SELECT MOD(29,9);
+-----------+
| mod(29,9) |
+-----------+
|         2 |
+-----------+
1 rows in set (0.00 sec)

This format is used instead:

mysql> SELECT MOD(29,9);
        -> 2

12.1. Operators

12.1.1. Operator Precedence

Operator precedences are shown in the following list, from lowest precedence to the highest. Operators that are shown together on a line have the same precedence.

:=
||, OR, XOR
&&, AND
NOT
BETWEEN, CASE, WHEN, THEN, ELSE
=, <=>, >=, >, <=, <, <>, !=, IS, LIKE, REGEXP, IN
|
&
<<, >>
-, +
*, /, DIV, %, MOD
^
- (unary minus), ~ (unary bit inversion)
!
BINARY, COLLATE

The precedence shown for NOT is as of MySQL 5.0.2. For earlier versions, or from 5.0.2 on if the HIGH_NOT_PRECEDENCE SQL mode is enabled, the precedence of NOT is the same as that of the ! operator. See Section 5.3.2, “The Server SQL Mode”.

12.1.2. Parentheses

  • ( ... )

    Use parentheses to force the order of evaluation in an expression. For example:

    mysql> SELECT 1+2*3;
            -> 7
    mysql> SELECT (1+2)*3;
            -> 9
    

12.1.3. Comparison Functions and Operators

Comparison operations result in a value of 1 (TRUE), 0 (FALSE), or NULL. These operations work for both numbers and strings. Strings are automatically converted to numbers and numbers to strings as necessary.

Some of the functions in this section (such as LEAST() and GREATEST()) return values other than 1 (TRUE), 0 (FALSE), or NULL. However, the value they return is based on comparison operations performed as described by the following rules.

MySQL compares values using the following rules:

  • If one or both arguments are NULL, the result of the comparison is NULL, except for the NULL-safe <=> equality comparison operator.

  • If both arguments in a comparison operation are strings, they are compared as strings.

  • If both arguments are integers, they are compared as integers.

  • Hexadecimal values are treated as binary strings if not compared to a number.

  • If one of the arguments is a TIMESTAMP or DATETIME column and the other argument is a constant, the constant is converted to a timestamp before the comparison is performed. This is done to be more ODBC-friendly. Note that this is not done for arguments in IN()! To be safe, always use complete datetime/date/time strings when doing comparisons.

  • In all other cases, the arguments are compared as floating-point (real) numbers.

By default, string comparisons are not case sensitive and use the current character set (cp1252 Latin1 by default, which also works well for English).

To convert a value to a specific type for comparison purposes, you can use the CAST() function. String values can be converted to a different character set using CONVERT(). See Section 12.8, “Cast Functions and Operators”.

The following examples illustrate conversion of strings to numbers for comparison operations:

mysql> SELECT 1 > '6x';
        -> 0
mysql> SELECT 7 > '6x';
        -> 1
mysql> SELECT 0 > 'x6';
        -> 0
mysql> SELECT 0 = 'x6';
        -> 1

Note that when you are comparing a string column with a number, MySQL cannot use an index on the column to look up the value quickly. If str_col is an indexed string column, the index cannot be used when performing the lookup in the following statement:

SELECT * FROM tbl_name WHERE str_col=1;

The reason for this is that there are many different strings that may convert to the value 1: '1', ' 1', '1a', ...

  • =

    Equal:

    mysql> SELECT 1 = 0;
            -> 0
    mysql> SELECT '0' = 0;
            -> 1
    mysql> SELECT '0.0' = 0;
            -> 1
    mysql> SELECT '0.01' = 0;
            -> 0
    mysql> SELECT '.01' = 0.01;
            -> 1
    
  • <=>

    NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operands are NULL, and 0 rather than NULL if one operand isNULL.

    mysql> SELECT 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
            -> 1, 1, 0
    mysql> SELECT 1 = 1, NULL = NULL, 1 = NULL;
            -> 1, NULL, NULL
    
  • <>, !=

    Not equal:

    mysql> SELECT '.01' <> '0.01';
            -> 1
    mysql> SELECT .01 <> '0.01';
            -> 0
    mysql> SELECT 'zapp' <> 'zappp';
            -> 1
    
  • <=

    Less than or equal:

    mysql> SELECT 0.1 <= 2;
            -> 1
    
  • <

    Less than:

    mysql> SELECT 2 < 2;
            -> 0
    
  • >=

    Greater than or equal:

    mysql> SELECT 2 >= 2;
            -> 1
    
  • >

    Greater than:

    mysql> SELECT 2 > 2;
            -> 0
    
  • IS boolean_value, IS NOT boolean_value

    Tests a value against a boolean value, where boolean_value can be TRUE, FALSE, or UNKNOWN.

    mysql> SELECT 1 IS TRUE, 0 IS FALSE, NULL IS UNKNOWN;
            -> 1, 1, 1
    mysql> SELECT 1 IS NOT UNKNOWN, 0 IS NOT UNKNOWN, NULL IS NOT UNKNOWN;
            -> 1, 1, 0
    

    IS [NOT] boolean_value syntax was added in MySQL 5.0.2.

  • IS NULL, IS NOT NULL

    Tests whether a value is or is not NULL.

    mysql> SELECT 1 IS NULL, 0 IS NULL, NULL IS NULL;
            -> 0, 0, 1
    mysql> SELECT 1 IS NOT NULL, 0 IS NOT NULL, NULL IS NOT NULL;
            -> 1, 1, 0
    

    To be able to work well with ODBC programs, MySQL supports the following extra features when using IS NULL:

    • You can find the row that contains the most recent AUTO_INCREMENT value by issuing a statement of the following form immediately after generating the value:

      SELECT * FROM tbl_name WHERE auto_col IS NULL
      

      This behavior can be disabled by setting SQL_AUTO_IS_NULL=0. See Section 13.5.3, “SET Syntax”.

    • For DATE and DATETIME columns that are declared as NOT NULL, you can find the special date '0000-00-00' by using a statement like this:

      SELECT * FROM tbl_name WHERE date_column IS NULL
      

      This is needed to get some ODBC applications to work because ODBC does not support a '0000-00-00' date value.

  • expr BETWEEN min AND max

    If expr is greater than or equal to min and expr is less than or equal to max, BETWEEN returns 1, otherwise it returns 0. This is equivalent to the expression (min <= expr AND expr <= max) if all the arguments are of the same type. Otherwise type conversion takes place according to the rules described at the beginning of this section, but applied to all the three arguments.

    mysql> SELECT 1 BETWEEN 2 AND 3;
            -> 0
    mysql> SELECT 'b' BETWEEN 'a' AND 'c';
            -> 1
    mysql> SELECT 2 BETWEEN 2 AND '3';
            -> 1
    mysql> SELECT 2 BETWEEN 2 AND 'x-3';
            -> 0
    
  • expr NOT BETWEEN min AND max

    This is the same as NOT (expr BETWEEN min AND max).

  • COALESCE(value,...)

    Returns the first non-NULL value in the list, or NULL if there are no non-NULL values.

    mysql> SELECT COALESCE(NULL,1);
            -> 1
    mysql> SELECT COALESCE(NULL,NULL,NULL);
            -> NULL
    
  • GREATEST(value1,value2,...)

    With two or more arguments, returns the largest (maximum-valued) argument. The arguments are compared using the same rules as for LEAST().

    mysql> SELECT GREATEST(2,0);
            -> 2
    mysql> SELECT GREATEST(34.0,3.0,5.0,767.0);
            -> 767.0
    mysql> SELECT GREATEST('B','A','C');
            -> 'C'
    

    Before MySQL 5.0.13, GREATEST() returns NULL only if all arguments are NULL. As of 5.0.13, it returns NULL if any argument is NULL.

  • expr IN (value,...)

    Returns 1 if expr is equal to any of the values in the IN list, else returns 0. If all values are constants, they are evaluated according to the type of expr and sorted. The search for the item then is done using a binary search. This means IN is very quick if the IN value list consists entirely of constants. Otherwise, type conversion takes place according to the rules described at the beginning of this section, but applied to all the arguments.

    mysql> SELECT 2 IN (0,3,5,'wefwf');
            -> 0
    mysql> SELECT 'wefwf' IN (0,3,5,'wefwf');
            -> 1
    

    The number of values in the IN list is only limited by the max_allowed_packet value.

    In order to comply with the SQL standard, IN returns NULL not only if the expression on the left hand side is NULL, but also if no match is found in the list and one of the expressions in the list is NULL.

    IN() syntax can also be used to write certain types of subqueries. See Section 13.2.8.3, “Subqueries with ANY, IN, and SOME.

  • expr NOT IN (value,...)

    This is the same as NOT (expr IN (value,...)).

  • ISNULL(expr)

    If expr is NULL, ISNULL() returns 1, otherwise it returns 0.

    mysql> SELECT ISNULL(1+1);
            -> 0
    mysql> SELECT ISNULL(1/0);
            -> 1
    

    A comparison of NULL values using = is always false.

    The ISNULL() function shares some special behaviors with the IS NULL comparison operator. See the description of IS NULL.

  • INTERVAL(N,N1,N2,N3,...)

    Returns 0 if N < N1, 1 if N < N2 and so on or -1 if N is NULL. All arguments are treated as integers. It is required that N1 < N2 < N3 < ... < Nn for this function to work correctly. This is because a binary search is used (very fast).

    mysql> SELECT INTERVAL(23, 1, 15, 17, 30, 44, 200);
            -> 3
    mysql> SELECT INTERVAL(10, 1, 10, 100, 1000);
            -> 2
    mysql> SELECT INTERVAL(22, 23, 30, 44, 200);
            -> 0
    
  • LEAST(value1,value2,...)

    With two or more arguments, returns the smallest (minimum-valued) argument. The arguments are compared using the following rules:

    • If the return value is used in an INTEGER context or all arguments are integer-valued, they are compared as integers.

    • If the return value is used in a REAL context or all arguments are real-valued, they are compared as reals.

    • If any argument is a case-sensitive string, the arguments are compared as case-sensitive strings.

    • In all other cases, the arguments are compared as case-insensitive strings.

    Before MySQL 5.0.13, LEAST() returns NULL only if all arguments are NULL. As of 5.0.13, it returns NULL if any argument is NULL.

    mysql> SELECT LEAST(2,0);
            -> 0
    mysql> SELECT LEAST(34.0,3.0,5.0,767.0);
            -> 3.0
    mysql> SELECT LEAST('B','A','C');
            -> 'A'
    

    Note that the preceding conversion rules can produce strange results in some borderline cases:

    mysql> SELECT CAST(LEAST(3600, 9223372036854775808.0) as SIGNED);
            -> -9223372036854775808
    

    This happens because MySQL reads 9223372036854775808.0 in an integer context. The integer representation is not good enough to hold the value, so it wraps to a signed integer.

12.1.4. Logical Operators

In SQL, all logical operators evaluate to TRUE, FALSE, or NULL (UNKNOWN). In MySQL, these are implemented as 1 (TRUE), 0 (FALSE), and NULL. Most of this is common to different SQL database servers, although some servers may return any non-zero value for TRUE.

  • NOT, !

    Logical NOT. Evaluates to 1 if the operand is 0, to 0 if the operand is non-zero, and NOT NULL returns NULL.

    mysql> SELECT NOT 10;
            -> 0
    mysql> SELECT NOT 0;
            -> 1
    mysql> SELECT NOT NULL;
            -> NULL
    mysql> SELECT ! (1+1);
            -> 0
    mysql> SELECT ! 1+1;
            -> 1
    

    The last example produces 1 because the expression evaluates the same way as (!1)+1.

    Note that the precedence of the NOT operator changed in MySQL 5.0.2. See Section 12.1.1, “Operator Precedence”.

  • AND, &&

    Logical AND. Evaluates to 1 if all operands are non-zero and not NULL, to 0 if one or more operands are 0, otherwise NULL is returned.

    mysql> SELECT 1 && 1;
            -> 1
    mysql> SELECT 1 && 0;
            -> 0
    mysql> SELECT 1 && NULL;
            -> NULL
    mysql> SELECT 0 && NULL;
            -> 0
    mysql> SELECT NULL && 0;
            -> 0
    
  • OR, ||

    Logical OR. When both operands are non-NULL, the result is 1 if any operand is non-zero, and 0 otherwise. With a NULL operand, the result is 1 if the other operand is non-zero, and NULL otherwise. If both operands are NULL, the result is NULL.

    mysql> SELECT 1 || 1;
            -> 1
    mysql> SELECT 1 || 0;
            -> 1
    mysql> SELECT 0 || 0;
            -> 0
    mysql> SELECT 0 || NULL;
            -> NULL
    mysql> SELECT 1 || NULL;
            -> 1
    
  • XOR

    Logical XOR. Returns NULL if either operand is NULL. For non-NULL operands, evaluates to 1 if an odd number of operands is non-zero, otherwise 0 is returned.

    mysql> SELECT 1 XOR 1;
            -> 0
    mysql> SELECT 1 XOR 0;
            -> 1
    mysql> SELECT 1 XOR NULL;
            -> NULL
    mysql> SELECT 1 XOR 1 XOR 1;
            -> 1
    

    a XOR b is mathematically equal to (a AND (NOT b)) OR ((NOT a) and b).

See also Section 12.1.1, “Operator Precedence”.

12.2. Control Flow Functions

  • CASE value WHEN [compare-value] THEN result [WHEN [compare-value] THEN result ...] [ELSE result] END

    CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END

    The first version returns the result where value=compare-value. The second version returns the result for the first condition that is true. If there was no matching result value, the result after ELSE is returned, or NULL if there is no ELSE part.

    mysql> SELECT CASE 1 WHEN 1 THEN 'one'
        ->     WHEN 2 THEN 'two' ELSE 'more' END;
            -> 'one'
    mysql> SELECT CASE WHEN 1>0 THEN 'true' ELSE 'false' END;
            -> 'true'
    mysql> SELECT CASE BINARY 'B'
        ->     WHEN 'a' THEN 1 WHEN 'b' THEN 2 END;
            -> NULL
    

    The default return type of a CASE expression is the compatible aggregated type of all return values, but also depends on the context in which it is used. If used in a string context, the result is returned as a string. If used in a numeric context, then the result is returned as a decimal, real, or integer value.

  • IF(expr1,expr2,expr3)

    If expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then IF() returns expr2; otherwise it returns expr3. IF() returns a numeric or string value, depending on the context in which it is used.

    mysql> SELECT IF(1>2,2,3);
            -> 3
    mysql> SELECT IF(1<2,'yes','no');
            -> 'yes'
    mysql> SELECT IF(STRCMP('test','test1'),'no','yes');
            -> 'no'
    

    If only one of expr2 or expr3 is explicitly NULL, the result type of the IF() function is the type of the non-NULL expression.

    expr1 is evaluated as an integer value, which means that if you are testing floating-point or string values, you should do so using a comparison operation.

    mysql> SELECT IF(0.1,1,0);
            -> 0
    mysql> SELECT IF(0.1<>0,1,0);
            -> 1
    

    In the first case shown, IF(0.1) returns 0 because 0.1 is converted to an integer value, resulting in a test of IF(0). This may not be what you expect. In the second case, the comparison tests the original floating-point value to see whether it is non-zero. The result of the comparison is used as an integer.

    The default return type of IF() (which may matter when it is stored into a temporary table) is calculated as follows:

    ExpressionReturn Value
    expr2 or expr3 returns a stringstring
    expr2 or expr3 returns a floating-point valuefloating-point
    expr2 or expr3 returns an integerinteger

    If expr2 and expr3 are both strings, the result is case sensitive if either string is case sensitive.

  • IFNULL(expr1,expr2)

    If expr1 is not NULL, IFNULL() returns expr1; otherwise it returns expr2. IFNULL() returns a numeric or string value, depending on the context in which it is used.

    mysql> SELECT IFNULL(1,0);
            -> 1
    mysql> SELECT IFNULL(NULL,10);
            -> 10
    mysql> SELECT IFNULL(1/0,10);
            -> 10
    mysql> SELECT IFNULL(1/0,'yes');
            -> 'yes'
    

    The default result value of IFNULL(expr1,expr2) is the more “general” of the two expressions, in the order STRING, REAL, or INTEGER. Consider the case of a table based on expressions or where MySQL must internally store a value returned by IFNULL() in a temporary table:

    CREATE TABLE tmp SELECT IFNULL(1,'test') AS test;
    

    In this example, the type of the test column is CHAR(4).

  • NULLIF(expr1,expr2)

    Returns NULL if expr1 = expr2 is true, otherwise returns expr1. This is the same as CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END.

    mysql> SELECT NULLIF(1,1);
            -> NULL
    mysql> SELECT NULLIF(1,2);
            -> 1
    

    Note that MySQL evaluates expr1 twice if the arguments are not equal.

12.3. String Functions

String-valued functions return NULL if the length of the result would be greater than the value of the max_allowed_packet system variable. See Section 7.5.2, “Tuning Server Parameters”.

For functions that operate on string positions, the first position is numbered 1.

  • ASCII(str)

    Returns the numeric value of the leftmost character of the string str. Returns 0 if str is the empty string. Returns NULL if str is NULL. ASCII() works for characters with numeric values from 0 to 255.

    mysql> SELECT ASCII('2');
            -> 50
    mysql> SELECT ASCII(2);
            -> 50
    mysql> SELECT ASCII('dx');
            -> 100
    

    See also the ORD() function.

  • BIN(N)

    Returns a string representation of the binary value of N, where N is a longlong (BIGINT) number. This is equivalent to CONV(N,10,2). Returns NULL if N is NULL.

    mysql> SELECT BIN(12);
            -> '1100'
    
  • BIT_LENGTH(str)

    Returns the length of the string str in bits.

    mysql> SELECT BIT_LENGTH('text');
            -> 32
    
  • CHAR(N,... [USING charset])

    CHAR() interprets each argument N as an integer and returns a string consisting of the characters given by the code values of those integers. NULL values are skipped.

    mysql> SELECT CHAR(77,121,83,81,'76');
            -> 'MySQL'
    mysql> SELECT CHAR(77,77.3,'77.3');
            -> 'MMM'
    

    As of MySQL 5.0.15, CHAR() arguments larger than 255 are converted into multiple result bytes. For example, CHAR(256) is equivalent to CHAR(1,0), and CHAR(256*256) is equivalent to CHAR(1,0,0):

    mysql> SELECT HEX(CHAR(1,0)), HEX(CHAR(256));
    +----------------+----------------+
    | HEX(CHAR(1,0)) | HEX(CHAR(256)) |
    +----------------+----------------+
    | 0100           | 0100           |
    +----------------+----------------+
    mysql> SELECT HEX(CHAR(1,0,0)), HEX(CHAR(256*256));
    +------------------+--------------------+
    | HEX(CHAR(1,0,0)) | HEX(CHAR(256*256)) |
    +------------------+--------------------+
    | 010000           | 010000             |
    +------------------+--------------------+
    

    CHAR() returns a binary string. To produce a string in a given character set, the optional USING clause may be used:

    mysql> SELECT CHARSET(CHAR(0x65)), CHARSET(CHAR(0x65 USING utf8));
    +---------------------+--------------------------------+
    | CHARSET(CHAR(0x65)) | CHARSET(CHAR(0x65 USING utf8)) |
    +---------------------+--------------------------------+
    | binary              | utf8                           |
    +---------------------+--------------------------------+
    

    If USING is given and the result string is illegal for the given character set, a warning is issued. Also if strict SQL mode is enabled, the result from CHAR() becomes NULL.

    Before MySQL 5.0.15, CHAR() returns a string in the connection character set and the USING clause is unavailable. In addition, each argument is interpreted modulo 256, so CHAR(256) and CHAR(256*256) both are equivalent to CHAR(0).

  • CHAR_LENGTH(str)

    Returns the length of the string str, measured in characters. A multi-byte character counts as a single character. This means that for a string containing five two-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.

  • CHARACTER_LENGTH(str)

    CHARACTER_LENGTH() is a synonym for CHAR_LENGTH().

  • COMPRESS(string_to_compress)

    Compresses a string. This function requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. The compressed string can be uncompressed with UNCOMPRESS().

    mysql> SELECT LENGTH(COMPRESS(REPEAT('a',1000)));
            -> 21
    mysql> SELECT LENGTH(COMPRESS(''));
            -> 0
    mysql> SELECT LENGTH(COMPRESS('a'));
            -> 13
    mysql> SELECT LENGTH(COMPRESS(REPEAT('a',16)));
            -> 15
    

    The compressed string contents are stored the following way:

    • Empty strings are stored as empty strings.

    • Non-empty strings are stored as a four-byte length of the uncompressed string (low byte first), followed by the compressed string. If the string ends with space, an extra ‘.’ character is added to avoid problems with endspace trimming should the result be stored in a CHAR or VARCHAR column. (Use of CHAR or VARCHAR to store compressed strings is not recommended. It is better to use a BLOB column instead.)

  • CONCAT(str1,str2,...)

    Returns the string that results from concatenating the arguments. Returns NULL if any argument is NULL. May have one or more arguments. If all arguments are non-binary strings, the result is a non-binary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent binary string form; if you want to avoid that you can use explicit type cast, like in this example: SELECT CONCAT(CAST(int_col AS CHAR), char_col)

    mysql> SELECT CONCAT('My', 'S', 'QL');
            -> 'MySQL'
    mysql> SELECT CONCAT('My', NULL, 'QL');
            -> NULL
    mysql> SELECT CONCAT(14.3);
            -> '14.3'
    
  • CONCAT_WS(separator,str1,str2,...)

    CONCAT_WS() stands for CONCAT With Separator and is a special form of CONCAT(). The first argument is the separator for the rest of the arguments. The separator is added between the strings to be concatenated. The separator can be a string as can the rest of the arguments. If the separator is NULL, the result is NULL. The function skips any NULL values after the separator argument.

    mysql> SELECT CONCAT_WS(',','First name','Second name','Last Name');
            -> 'First name,Second name,Last Name'
    mysql> SELECT CONCAT_WS(',','First name',NULL,'Last Name');
            -> 'First name,Last Name'
    

    CONCAT_WS() does not skip empty strings. (However, it does skip NULLs.)

  • CONV(N,from_base,to_base)

    Converts numbers between different number bases. Returns a string representation of the number N, converted from base from_base to base to_base. Returns NULL if any argument is NULL. The argument N is interpreted as an integer, but may be specified as an integer or a string. The minimum base is 2 and the maximum base is 36. If to_base is a negative number, N is regarded as a signed number. Otherwise, N is treated as unsigned. CONV() works with 64-bit precision.

    mysql> SELECT CONV('a',16,2);
            -> '1010'
    mysql> SELECT CONV('6E',18,8);
            -> '172'
    mysql> SELECT CONV(-17,10,-18);
            -> '-H'
    mysql> SELECT CONV(10+'10'+'10'+0xa,10,10);
            -> '40'
    
  • ELT(N,str1,str2,str3,...)

    Returns str1 if N = 1, str2 if N = 2, and so on. Returns NULL if N is less than 1 or greater than the number of arguments. ELT() is the complement of FIELD().

    mysql> SELECT ELT(1, 'ej', 'Heja', 'hej', 'foo');
            -> 'ej'
    mysql> SELECT ELT(4, 'ej', 'Heja', 'hej', 'foo');
            -> 'foo'
    
  • EXPORT_SET(bits,on,off[,separator[,number_of_bits]])

    Returns a string in which for every bit set in the value bits, you get an on string and for every reset bit you get an off string. Bits in bits are examined from right to left (from low-order to high-order bits). Strings are added to the result from left to right, separated by the separator string (the default being the comma character ‘,’). The number of bits examined is given by number_of_bits (defaults to 64).

    mysql> SELECT EXPORT_SET(5,'Y','N',',',4);
            -> 'Y,N,Y,N'
    mysql> SELECT EXPORT_SET(6,'1','0',',',10);
            -> '0,1,1,0,0,0,0,0,0,0'
    
  • FIELD(str,str1,str2,str3,...)

    Returns the index of str in the str1, str2, str3, ... list. Returns 0 if str is not found.

    If all arguments to FIELD() are strings, all arguments are compared as strings. If all arguments are numbers, they are compared as numbers. Otherwise, the arguments are compared as double.

    If str is NULL, the return value is 0 because NULL fails equality comparison with any value. FIELD() is the complement of ELT().

    mysql> SELECT FIELD('ej', 'Hej', 'ej', 'Heja', 'hej', 'foo');
            -> 2
    mysql> SELECT FIELD('fo', 'Hej', 'ej', 'Heja', 'hej', 'foo');
            -> 0
    
  • FIND_IN_SET(str,strlist)

    Returns a value in the range of 1 to N if the string str is in the string list strlist consisting of N substrings. A string list is a string composed of substrings separated by ‘,’ characters. If the first argument is a constant string and the second is a column of type SET, the FIND_IN_SET() function is optimized to use bit arithmetic. Returns 0 if str is not in strlist or if strlist is the empty string. Returns NULL if either argument is NULL. This function does not work properly if the first argument contains a comma (‘,’) character.

    mysql> SELECT FIND_IN_SET('b','a,b,c,d');
            -> 2
    
  • FORMAT(X,D)

    Formats the number X to a format like '#,###,###.##', rounded to D decimals, and returns the result as a string. See For details, see Section 12.9.4, “Miscellaneous Functions”.

  • HEX(N_or_S)

    If N_OR_S is a number, returns a string representation of the hexadecimal value of N, where N is a longlong (BIGINT) number. This is equivalent to CONV(N,10,16).

    If N_OR_S is a string, returns a hexadecimal string representation of N_OR_S where each character in N_OR_S is converted to two hexadecimal digits.

    mysql> SELECT HEX(255);
            -> 'FF'
    mysql> SELECT 0x616263;
            -> 'abc'
    mysql> SELECT HEX('abc');
            -> 616263
    
  • INSERT(str,pos,len,newstr)

    Returns the string str, with the substring beginning at position pos and len characters long replaced by the string newstr. Returns the original string if pos is not within the length of the string. Replaces the rest of the string from position pos is len is not within the length of the rest of the string. Returns NULL if any argument is null.

    mysql> SELECT INSERT('Quadratic', 3, 4, 'What');
            -> 'QuWhattic'
    mysql> SELECT INSERT('Quadratic', -1, 4, 'What');
            -> 'Quadratic'
    mysql> SELECT INSERT('Quadratic', 3, 100, 'What');
            -> 'QuWhat'
    

    This function is multi-byte safe.

  • INSTR(str,substr)

    Returns the position of the first occurrence of substring substr in string str. This is the same as the two-argument form of LOCATE(), except that the order of the arguments is reversed.

    mysql> SELECT INSTR('foobarbar', 'bar');
            -> 4
    mysql> SELECT INSTR('xbar', 'foobar');
            -> 0
    

    This function is multi-byte safe, and is case sensitive only if at least one argument is a binary string.

  • LCASE(str)

    LCASE() is a synonym for LOWER().

  • LEFT(str,len)

    Returns the leftmost len characters from the string str.

    mysql> SELECT LEFT('foobarbar', 5);
            -> 'fooba'
    
  • LENGTH(str)

    Returns the length of the string str, measured in bytes. A multi-byte character counts as multiple bytes. This means that for a string containing five two-byte characters, LENGTH() returns 10, whereas CHAR_LENGTH() returns 5.

    mysql> SELECT LENGTH('text');
            -> 4
    
  • LOAD_FILE(file_name)

    Reads the file and returns the file contents as a string. The file must be located on the server, you must specify the full pathname to the file, and you must have the FILE privilege. The file must be readable by all and its size less than max_allowed_packet bytes.

    If the file does not exist or cannot be read because one of the preceding conditions is not satisfied, the function returns NULL.

    mysql> UPDATE tbl_name
               SET blob_column=LOAD_FILE('/tmp/picture')
               WHERE id=1;
    
  • LOCATE(substr,str) , LOCATE(substr,str,pos)

    The first syntax returns the position of the first occurrence of substring substr in string str. The second syntax returns the position of the first occurrence of substring substr in string str, starting at position pos. Returns 0 if substr is not in str.

    mysql> SELECT LOCATE('bar', 'foobarbar');
            -> 4
    mysql> SELECT LOCATE('xbar', 'foobar');
            -> 0
    mysql> SELECT LOCATE('bar', 'foobarbar',5);
            -> 7
    

    This function is multi-byte safe, and is case-sensitive only if at least one argument is a binary string.

  • LOWER(str)

    Returns the string str with all characters changed to lowercase according to the current character set mapping (the default is cp1252 Latin1).

    mysql> SELECT LOWER('QUADRATICALLY');
            -> 'quadratically'
    

    This function is multi-byte safe.

  • LPAD(str,len,padstr)

    Returns the string str, left-padded with the string padstr to a length of len characters. If str is longer than len, the return value is shortened to len characters.

    mysql> SELECT LPAD('hi',4,'??');
            -> '??hi'
    mysql> SELECT LPAD('hi',1,'??');
            -> 'h'
    
  • LTRIM(str)

    Returns the string str with leading space characters removed.

    mysql> SELECT LTRIM('  barbar');
            -> 'barbar'
    

    This function is multi-byte safe.

  • MAKE_SET(bits,str1,str2,...)

    Returns a set value (a string containing substrings separated by ‘,’ characters) consisting of the strings that have the corresponding bit in bits set. str1 corresponds to bit 0, str2 to bit 1, and so on. NULL values in str1, str2, ... are not appended to the result.

    mysql> SELECT MAKE_SET(1,'a','b','c');
            -> 'a'
    mysql> SELECT MAKE_SET(1 | 4,'hello','nice','world');
            -> 'hello,world'
    mysql> SELECT MAKE_SET(1 | 4,'hello','nice',NULL,'world');
            -> 'hello'
    mysql> SELECT MAKE_SET(0,'a','b','c');
            -> ''
    
  • MID(str,pos,len)

    MID(str,pos,len) is a synonym for SUBSTRING(str,pos,len).

  • OCT(N)

    Returns a string representation of the octal value of N, where N is a longlong (BIGINT)number. This is equivalent to CONV(N,10,8). Returns NULL if N is NULL.

    mysql> SELECT OCT(12);
            -> '14'
    
  • OCTET_LENGTH(str)

    OCTET_LENGTH() is a synonym for LENGTH().

  • ORD(str)

    If the leftmost character of the string str is a multi-byte character, returns the code for that character, calculated from the numeric values of its constituent bytes using this formula:

      (1st byte code)
    + (2nd byte code × 256)
    + (3rd byte code × 2562) ...
    

    If the leftmost character is not a multi-byte character, ORD() returns the same value as the ASCII() function.

    mysql> SELECT ORD('2');
            -> 50
    
  • POSITION(substr IN str)

    POSITION(substr IN str) is a synonym for LOCATE(substr,str).

  • QUOTE(str)

    Quotes a string to produce a result that can be used as a properly escaped data value in an SQL statement. The string is returned surrounded by single quotes and with each instance of single quote (‘'’), backslash (‘\’), ASCII NUL, and Control-Z preceded by a backslash. If the argument is NULL, the return value is the word “NULL” without surrounding single quotes.

    mysql> SELECT QUOTE('Don\'t!');
            -> 'Don\'t!'
    mysql> SELECT QUOTE(NULL);
            -> NULL
    
  • REPEAT(str,count)

    Returns a string consisting of the string str repeated count times. If count <= 0, returns an empty string. Returns NULL if str or count are NULL.

    mysql> SELECT REPEAT('MySQL', 3);
            -> 'MySQLMySQLMySQL'
    
  • REPLACE(str,from_str,to_str)

    Returns the string str with all occurrences of the string from_str replaced by the string to_str. REPLACE() performs a case-sensitive match when searching for from_str.

    mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww');
            -> 'WwWwWw.mysql.com'
    

    This function is multi-byte safe.

  • REVERSE(str)

    Returns the string str with the order of the characters reversed.

    mysql> SELECT REVERSE('abc');
            -> 'cba'
    

    This function is multi-byte safe.

  • RIGHT(str,len)

    Returns the rightmost len characters from the string str.

    mysql> SELECT RIGHT('foobarbar', 4);
            -> 'rbar'
    

    This function is multi-byte safe.

  • RPAD(str,len,padstr)

    Returns the string str, right-padded with the string padstr to a length of len characters. If str is longer than len, the return value is shortened to len characters.

    mysql> SELECT RPAD('hi',5,'?');
            -> 'hi???'
    mysql> SELECT RPAD('hi',1,'?');
            -> 'h'
    

    This function is multi-byte safe.

  • RTRIM(str)

    Returns the string str with trailing space characters removed.

    mysql> SELECT RTRIM('barbar   ');
            -> 'barbar'
    

    This function is multi-byte safe.

  • SOUNDEX(str)

    Returns a soundex string from str. Two strings that sound almost the same should have identical soundex strings. A standard soundex string is four characters long, but the SOUNDEX() function returns an arbitrarily long string. You can use SUBSTRING() on the result to get a standard soundex string. All non-alphabetic characters in str are ignored. All international alphabetic characters outside the A-Z range are treated as vowels.

    mysql> SELECT SOUNDEX('Hello');
            -> 'H400'
    mysql> SELECT SOUNDEX('Quadratically');
            -> 'Q36324'
    

    Note: This function implements the original Soundex algorithm, not the more popular enhanced version (also described by D. Knuth). The difference is that original version discards vowels first and then duplicates, whereas the enhanced version discards duplicates first and then vowels.

  • expr1 SOUNDS LIKE expr2

    This is the same as SOUNDEX(expr1) = SOUNDEX(expr2).

  • SPACE(N)

    Returns a string consisting of N space characters.

    mysql> SELECT SPACE(6);
            -> '      '
    
  • SUBSTRING(str,pos) , SUBSTRING(str FROM pos) SUBSTRING(str,pos,len) , SUBSTRING(str FROM pos FOR len)

    The forms without a len argument return a substring from string str starting at position pos. The forms with a len argument return a substring len characters long from string str, starting at position pos. The forms that use FROM are standard SQL syntax. It is also possible to use a negative value for pos. In this case, the beginning of the substring is pos characters from the end of the string, rather than the beginning. A negative value may be used for pos in any of the forms of this function.

    mysql> SELECT SUBSTRING('Quadratically',5);
            -> 'ratically'
    mysql> SELECT SUBSTRING('foobarbar' FROM 4);
            -> 'barbar'
    mysql> SELECT SUBSTRING('Quadratically',5,6);
            -> 'ratica'        
    mysql> SELECT SUBSTRING('Sakila', -3);
            -> 'ila'        
    mysql> SELECT SUBSTRING('Sakila', -5, 3);
            -> 'aki'
    mysql> SELECT SUBSTRING('Sakila' FROM -4 FOR 2);
            -> 'ki'
    

    This function is multi-byte safe.

    Note that if you use a value less than than 1 for len, the result is always an empty string.

    SUBSTR() is a synonym for SUBSTRING().

  • SUBSTRING_INDEX(str,delim,count)

    Returns the substring from string str before count occurrences of the delimiter delim. If count is positive, everything to the left of the final delimiter (counting from the left) is returned. If count is negative, everything to the right of the final delimiter (counting from the right) is returned. SUBSTRING_INDEX() performs a case-sensitive match when searching for delim.

    mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2);
            -> 'www.mysql'
    mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2);
            -> 'mysql.com'
    

    This function is multi-byte safe.

  • TRIM([{BOTH | LEADING | TRAILING} [remstr] FROM] str) TRIM(remstr FROM] str)

    Returns the string str with all remstr prefixes and/or suffixes removed. If none of the specifiers BOTH, LEADING, or TRAILING is given, BOTH is assumed. remstr is optional and, if not specified, spaces are removed.

    mysql> SELECT TRIM('  bar   ');
            -> 'bar'
    mysql> SELECT TRIM(LEADING 'x' FROM 'xxxbarxxx');
            -> 'barxxx'
    mysql> SELECT TRIM(BOTH 'x' FROM 'xxxbarxxx');
            -> 'bar'
    mysql> SELECT TRIM(TRAILING 'xyz' FROM 'barxxyz');
            -> 'barx'
    

    This function is multi-byte safe.

  • UCASE(str)

    UCASE() is a synonym for UPPER().

  • UNCOMPRESS(string_to_uncompress)

    Uncompresses a string compressed by the COMPRESS() function. If the argument is not a compressed value, the result is NULL. This function requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL.

    mysql> SELECT UNCOMPRESS(COMPRESS('any string'));
            -> 'any string'
    mysql> SELECT UNCOMPRESS('any string');
            -> NULL
    
  • UNCOMPRESSED_LENGTH(compressed_string)

    Returns the length of a compressed string before compression.

    mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT('a',30)));
            -> 30
    
  • UNHEX(str)

    Performs the opposite operation from HEX(str). That is, it interprets each pair of hexadecimal digits in the argument as a number and converts it to the character represented by the number. The resulting characters are returned as a binary string.

    mysql> SELECT UNHEX('4D7953514C');
            -> 'MySQL'
    mysql> SELECT 0x4D7953514C;
            -> 'MySQL'
    mysql> SELECT UNHEX(HEX('string'));
            -> 'string'
    mysql> SELECT HEX(UNHEX('1267'));
            -> '1267'
    
  • UPPER(str)

    Returns the string str with all characters changed to uppercase according to the current character set mapping (the default is cp1252 Latin1).

    mysql> SELECT UPPER('Hej');
            -> 'HEJ'
    

    This function is multi-byte safe.

12.3.1. String Comparison Functions

MySQL automatically converts numbers to strings as necessary, and vice versa.

mysql> SELECT 1+'1';
        -> 2
mysql> SELECT CONCAT(2,' test');
        -> '2 test'

If you want to convert a number to a string explicitly, use the CAST() or CONCAT() function:

mysql> SELECT 38.8, CAST(38.8 AS CHAR);
        -> 38.8, '38.8'
mysql> SELECT 38.8, CONCAT(38.8);
        -> 38.8, '38.8'

CAST() is preferable.

If a string function is given a binary string as an argument, the resulting string is also a binary string. A number converted to a string is treated as a binary string. This affects only comparisons.

Normally, if any expression in a string comparison is case sensitive, the comparison is performed in case-sensitive fashion.

  • expr LIKE pat [ESCAPE 'escape-char']

    Pattern matching using SQL simple regular expression comparison. Returns 1 (TRUE) or 0 (FALSE). If either expr or pat is NULL, the result is NULL.

    The pattern need not be a literal string. For example, it can be specified as a string expression or table column.

    Per the SQL standard, LIKE performs matching on a per-character basis, thus it can have different results than the = comparison operator:

    mysql> SELECT 'ä' LIKE 'ae' COLLATE latin1_german2_ci;
    +-----------------------------------------+
    | 'ä' LIKE 'ae' COLLATE latin1_german2_ci |
    +-----------------------------------------+
    |                                       0 |
    +-----------------------------------------+
    mysql> SELECT 'ä' = 'ae' COLLATE latin1_german2_ci;
    +--------------------------------------+
    | 'ä' = 'ae' COLLATE latin1_german2_ci |
    +--------------------------------------+
    |                                    1 |
    +--------------------------------------+
    

    With LIKE you can use the following two wildcard characters in the pattern:

    CharacterDescription
    %Matches any number of characters, even zero characters
    _Matches exactly one character
    mysql> SELECT 'David!' LIKE 'David_';
            -> 1
    mysql> SELECT 'David!' LIKE '%D%v%';
            -> 1
    

    To test for literal instances of a wildcard character, precede the character with the escape character. If you do not specify the ESCAPE character, ‘\’ is assumed.

    StringDescription
    \%Matches one ‘%’ character
    \_Matches one ‘_’ character
    mysql> SELECT 'David!' LIKE 'David\_';
            -> 0
    mysql> SELECT 'David_' LIKE 'David\_';
            -> 1
    

    To specify a different escape character, use the ESCAPE clause:

    mysql> SELECT 'David_' LIKE 'David|_' ESCAPE '|';
            -> 1
    

    The escape sequence should be empty or one character long. As of MySQL 5.0.16, if the NO_BACKSLASH_ESCAPES SQL mode is enabled, the sequence cannot be empty.

    The following two statements illustrate that string comparisons are not case sensitive unless one of the operands is a binary string:

    mysql> SELECT 'abc' LIKE 'ABC';
            -> 1
    mysql> SELECT 'abc' LIKE BINARY 'ABC';
            -> 0
    

    In MySQL, LIKE is allowed on numeric expressions. (This is an extension to the standard SQL LIKE.)

    mysql> SELECT 10 LIKE '1%';
            -> 1
    

    Note: Because MySQL uses C escape syntax in strings (for example, ‘\n’ to represent a newline character), you must double any ‘\’ that you use in LIKE strings. For example, to search for ‘\n’, specify it as ‘\\n’. To search for ‘\’, specify it as ‘\\\\’; this is because the backslashes are stripped once by the parser and again when the pattern match is made, leaving a single backslash to be matched against.

  • expr NOT LIKE pat [ESCAPE 'escape-char']

    This is the same as NOT (expr LIKE pat [ESCAPE 'escape-char']).

  • expr NOT REGEXP pat expr NOT RLIKE pat

    This is the same as NOT (expr REGEXP pat).

  • expr REGEXP pat expr RLIKE pat

    Performs a pattern match of a string expression expr against a pattern pat. The pattern can be an extended regular expression. The syntax for regular expressions is discussed in Appendix G, MySQL Regular Expressions. Returns 1 if expr matches pat; otherwise it returns 0. If either expr or pat is NULL, the result is NULL. RLIKE is a synonym for REGEXP, provided for mSQL compatibility.

    The pattern need not be a literal string. For example, it can be specified as a string expression or table column.

    Note: Because MySQL uses the C escape syntax in strings (for example, ‘\n’ to represent the newline character), you must double any ‘\’ that you use in your REGEXP strings.

    REGEXP is not case sensitive, except when used with binary strings.

    mysql> SELECT 'Monty!' REGEXP 'm%y%%';
            -> 0
    mysql> SELECT 'Monty!' REGEXP '.*';
            -> 1
    mysql> SELECT 'new*\n*line' REGEXP 'new\\*.\\*line';
            -> 1
    mysql> SELECT 'a' REGEXP 'A', 'a' REGEXP BINARY 'A';
            -> 1  0
    mysql> SELECT 'a' REGEXP '^[a-d]';
            -> 1
    

    REGEXP and RLIKE use the current character set (cp1252 Latin1 by default) when deciding the type of a character. Warning: These operators are not multi-byte safe.

  • STRCMP(expr1,expr2)

    STRCMP() returns 0 if the strings are the same, -1 if the first argument is smaller than the second according to the current sort order, and 1 otherwise.

    mysql> SELECT STRCMP('text', 'text2');
            -> -1
    mysql> SELECT STRCMP('text2', 'text');
            -> 1
    mysql> SELECT STRCMP('text', 'text');
            -> 0
    

    STRCMP() uses the current character set when performing comparisons. This makes the default comparison behavior case insensitive unless one or both of the operands are binary strings.

12.4. Numeric Functions

12.4.1. Arithmetic Operators

The usual arithmetic operators are available. Note that in the case of -, +, and *, the result is calculated with BIGINT (64-bit) precision if both arguments are integers. If one of the arguments is an unsigned integer, and the other argument is also an integer, the result is an unsigned integer. See Section 12.8, “Cast Functions and Operators”.

  • +

    Addition:

    mysql> SELECT 3+5;
            -> 8
    
  • -

    Subtraction:

    mysql> SELECT 3-5;
            -> -2
    
  • -

    Unary minus. Changes the sign of the argument.

    mysql> SELECT - 2;
            -> -2
    

    Note: If this operator is used with a BIGINT, the return value is also a BIGINT. This means that you should avoid using on integers that may have the value of –263.

  • *

    Multiplication:

    mysql> SELECT 3*5;
            -> 15
    mysql> SELECT 18014398509481984*18014398509481984.0;
            -> 324518553658426726783156020576256.0
    mysql> SELECT 18014398509481984*18014398509481984;
            -> 0
    

    The result of the last expression is incorrect because the result of the integer multiplication exceeds the 64-bit range of BIGINT calculations. (See Section 11.2, “Numeric Types”.)

  • /

    Division:

    mysql> SELECT 3/5;
            -> 0.60
    

    Division by zero produces a NULL result:

    mysql> SELECT 102/(1-1);
            -> NULL
    

    A division is calculated with BIGINT arithmetic only if performed in a context where its result is converted to an integer.

  • DIV

    Integer division. Similar to FLOOR() but safe with BIGINT values.

    mysql> SELECT 5 DIV 2;
            -> 2
    

12.4.2. Mathematical Functions

All mathematical functions return NULL in the event of an error.

  • ABS(X)

    Returns the absolute value of X.

    mysql> SELECT ABS(2);
            -> 2
    mysql> SELECT ABS(-32);
            -> 32
    

    This function is safe to use with BIGINT values.

  • ACOS(X)

    Returns the arc cosine of X, that is, the value whose cosine is X. Returns NULL if X is not in the range -1 to 1.

    mysql> SELECT ACOS(1);
            -> 0
    mysql> SELECT ACOS(1.0001);
            -> NULL
    mysql> SELECT ACOS(0);
            -> 1.5707963267949
    
  • ASIN(X)

    Returns the arc sine of X, that is, the value whose sine is X. Returns NULL if X is not in the range -1 to 1.

    mysql> SELECT ASIN(0.2);
            -> 0.20135792079033
    mysql> SELECT ASIN('foo');
    
    +-------------+
    | ASIN('foo') |
    +-------------+
    |           0 |
    +-------------+
    1 row in set, 1 warning (0.00 sec)
    
    mysql> SHOW WARNINGS;
    +---------+------+-----------------------------------------+
    | Level   | Code | Message                                 |
    +---------+------+-----------------------------------------+
    | Warning | 1292 | Truncated incorrect DOUBLE value: 'foo' |
    +---------+------+-----------------------------------------+
    
  • ATAN(X)

    Returns the arc tangent of X, that is, the value whose tangent is X.

    mysql> SELECT ATAN(2);
            -> 1.1071487177941
    mysql> SELECT ATAN(-2);
            -> -1.1071487177941
    
  • ATAN(Y,X) , ATAN2(Y,X)

    Returns the arc tangent of the two variables X and Y. It is similar to calculating the arc tangent of Y / X, except that the signs of both arguments are used to determine the quadrant of the result.

    mysql> SELECT ATAN(-2,2);
            -> -0.78539816339745
    mysql> SELECT ATAN2(PI(),0);
            -> 1.5707963267949
    
  • CEILING(X) CEIL(X)

    Returns the smallest integer value not less than X.

    mysql> SELECT CEILING(1.23);
            -> 2
    mysql> SELECT CEIL(-1.23);
            -> -1
    

    These two functions are synonymous. Note that the return value is converted to a BIGINT.

  • COS(X)

    Returns the cosine of X, where X is given in radians.

    mysql> SELECT COS(PI());
            -> -1
    
  • COT(X)

    Returns the cotangent of X.

    mysql> SELECT COT(12);
            -> -1.5726734063977
    mysql> SELECT COT(0);
            -> NULL
    
  • CRC32(expr)

    Computes a cyclic redundancy check value and returns a 32-bit unsigned value. The result is NULL if the argument is NULL. The argument is expected to be a string and (if possible) is treated as one if it is not.

    mysql> SELECT CRC32('MySQL');
            -> 3259397556
    mysql> SELECT CRC32('mysql');
            -> 2501908538
    
  • DEGREES(X)

    Returns the argument X, converted from radians to degrees.

    mysql> SELECT DEGREES(PI());
            -> 180
    mysql> SELECT DEGREES(PI() / 2);
            -> 90
    
  • EXP(X)

    Returns the value of e (the base of natural logarithms) raised to the power of X.

    mysql> SELECT EXP(2);
            -> 7.3890560989307
    mysql> SELECT EXP(-2);
            -> 0.13533528323661
    mysql> SELECT EXP(0);
            -> 1
    
  • FLOOR(X)

    Returns the largest integer value not greater than X.

    mysql> SELECT FLOOR(1.23);
            -> 1
    mysql> SELECT FLOOR(-1.23);
            -> -2
    

    Note that the return value is converted to a BIGINT.

  • FORMAT(X,D)

    Formats the number X to a format like '#,###,###.##', rounded to D decimals, and returns the result as a string. See For details, see Section 12.9.4, “Miscellaneous Functions”.

  • LN(X)

    Returns the natural logarithm of X, that is, the logarithm of X to the base e.

    mysql> SELECT LN(2);
            -> 0.69314718055995
    mysql> SELECT LN(-2);
            -> NULL
    

    This function is synonymous with LOG(X).

  • LOG(X) LOG(B,X)

    If called with one parameter, this function returns the natural logarithm of X.

    mysql> SELECT LOG(2);
            -> 0.69314718055995
    mysql> SELECT LOG(-2);
            -> NULL
    

    If called with two parameters, this function returns the logarithm of X for an arbitrary base B.

    mysql> SELECT LOG(2,65536);
            -> 16
    mysql> SELECT LOG(10,100);
            -> 2
    

    LOG(B,X) is equivalent to LOG(X) / LOG(B).

  • LOG2(X)

    Returns the base-2 logarithm of X.

    mysql> SELECT LOG2(65536);
            -> 16
    mysql> SELECT LOG2(-100);
            -> NULL
    

    LOG2() is useful for finding out how many bits a number requires for storage. This function is equivalent to the expression LOG(X) / LOG(2).

  • LOG10(X)

    Returns the base-10 logarithm of X.

    mysql> SELECT LOG10(2);
            -> 0.30102999566398
    mysql> SELECT LOG10(100);
            -> 2
    mysql> SELECT LOG10(-100);
            -> NULL
    

    LOG10(X) is equivalent to LOG(10,X).

  • MOD(N,M) , N % M N MOD M

    Modulo operation. Returns the remainder of N divided by M.

    mysql> SELECT MOD(234, 10);
            -> 4
    mysql> SELECT 253 % 7;
            -> 1
    mysql> SELECT MOD(29,9);
            -> 2
    mysql> SELECT 29 MOD 9;
            -> 2
    

    This function is safe to use with BIGINT values.

    MOD() also works on values with a fractional part and returns the exact remainder after division:

    mysql> SELECT MOD(34.5,3);
            -> 1.5
    
  • PI()

    Returns the value of ϖ (pi). The default number of decimals displayed is seven, but MySQL internally uses the full double-precision value.

    mysql> SELECT PI();
            -> 3.141593
    mysql> SELECT PI()+0.000000000000000000;
            -> 3.141592653589793116
    
  • POW(X,Y) , POWER(X,Y)

    Returns the value of X raised to the power of Y.

    mysql> SELECT POW(2,2);
            -> 4
    mysql> SELECT POW(2,-2);
            -> 0.25
    
  • RADIANS(X)

    Returns the argument X, converted from degrees to radians. (Note that ϖ radians equals 180 degrees.)

    mysql> SELECT RADIANS(90);
            -> 1.5707963267949
    
  • RAND() RAND(N)

    Returns a random floating-point value v between 0 and 1 inclusive (that is, in the range 0v1.0). If an integer argument N is specified, it is used as the seed value, which produces a repeatable sequence.

    mysql> SELECT RAND();
            -> 0.9233482386203
    mysql> SELECT RAND(20);
            -> 0.15888261251047
    mysql> SELECT RAND(20);
            -> 0.15888261251047
    mysql> SELECT RAND();
            -> 0.63553050033332
    mysql> SELECT RAND();
            -> 0.70100469486881
    mysql> SELECT RAND(20);
            -> 0.15888261251047
    

    To obtain a random integer R in the range iRj, use the expression FLOOR(i + RAND() * (ji + 1)). For example, to obtain a random integer in the range of 7 to 12 inclusive, you could use the following statement:

    SELECT FLOOR(7 + (RAND() * 6));
    

    You cannot use a column with RAND() values in an ORDER BY clause, because ORDER BY would evaluate the column multiple times. However, you can retrieve rows in random order like this:

    mysql> SELECT * FROM tbl_name ORDER BY RAND();
    

    ORDER BY RAND() combined with LIMIT is useful for selecting a random sample from a set of rows:

    mysql> SELECT * FROM table1, table2 WHERE a=b AND c<d
        -> ORDER BY RAND() LIMIT 1000;
    

    Note that RAND() in a WHERE clause is re-evaluated every time the WHERE is executed.

    RAND() is not meant to be a perfect random generator, but instead is a fast way to generate ad hoc random numbers which is portable between platforms for the same MySQL version.

  • ROUND(X) ROUND(X,D)

    Returns the argument X, rounded to the nearest integer. With two arguments, returns X rounded to D decimals. D can be negative in order to round D digits left of the decimal point of the value X.

    mysql> SELECT ROUND(-1.23);
            -> -1
    mysql> SELECT ROUND(-1.58);
            -> -2
    mysql> SELECT ROUND(1.58);
            -> 2
    mysql> SELECT ROUND(1.298, 1);
            -> 1.3
    mysql> SELECT ROUND(1.298, 0);
            -> 1
    mysql> SELECT ROUND(23.298, -1);
            -> 20
    

    The return type is the same type as that of the first argument (assuming that it is integer, double, or decimal). This means that for an integer argument, the result is an integer (no decimals).

    Before MySQL 5.0.3, the behavior of ROUND() when the argument is halfway between two integers depends on the C library implementation. Different implementations round to the nearest even number, always up, always down, or always toward zero. If you need one kind of rounding, you should use a well-defined function such as TRUNCATE() or FLOOR() instead.

    As of MySQL 5.0.3, ROUND() uses the precision math library for exact-value arguments when the first argument is a decimal value:

    • For exact-value numbers, ROUND() uses the “round half up” or “round toward nearest” rule: A value with a fractional part of .5 or greater is rounded up to the next integer if positive or down to the next integer if negative. (In other words, it is rounded away from zero.) A value with a fractional part less than .5 is rounded down to the next integer if positive or up to the next integer if negative.

    • For approximate-value numbers, the result depends on the C library. On many systems, this means that ROUND() uses the "round to nearest even" rule: A value with any fractional part is rounded to the nearest even integer.

    The following example shows how rounding differs for exact and approximate values:

    mysql> SELECT ROUND(2.5), ROUND(25E-1);
    +------------+--------------+
    | ROUND(2.5) | ROUND(25E-1) |
    +------------+--------------+
    | 3          |            2 |
    +------------+--------------+
    

    For more information, see Chapter 21, Precision Math.

  • SIGN(X)

    Returns the sign of the argument as -1, 0, or 1, depending on whether X is negative, zero, or positive.

    mysql> SELECT SIGN(-32);
            -> -1
    mysql> SELECT SIGN(0);
            -> 0
    mysql> SELECT SIGN(234);
            -> 1
    
  • SIN(X)

    Returns the sine of X, where X is given in radians.

    mysql> SELECT SIN(PI());
            -> 1.2246063538224e-16
    mysql> SELECT ROUND(SIN(PI()));
            -> 0
    
  • SQRT(X)

    Returns the square root of a non-negative number X.

    mysql> SELECT SQRT(4);
            -> 2
    mysql> SELECT SQRT(20);
            -> 4.4721359549996
    mysql> SELECT SQRT(-16);
            -> NULL        
    
  • TAN(X)

    Returns the tangent of X, where X is given in radians.

    mysql> SELECT TAN(PI());
            -> -1.2246063538224e-16
    mysql> SELECT TAN(PI()+1);
            -> 1.5574077246549
    
  • TRUNCATE(X,D)

    Returns the number X, truncated to D decimals. If D is 0, the result has no decimal point or fractional part. D can be negative in order to truncate (make zero) D digits left of the decimal point of the value X.

    mysql> SELECT TRUNCATE(1.223,1);
            -> 1.2
    mysql> SELECT TRUNCATE(1.999,1);
            -> 1.9
    mysql> SELECT TRUNCATE(1.999,0);
            -> 1
    mysql> SELECT TRUNCATE(-1.999,1);
            -> -1.9
    mysql> SELECT TRUNCATE(122,-2);
           -> 100
    mysql> SELECT TRUNCATE(10.28*100,0);
           -> 1028
    

    All numbers are rounded toward zero.

12.5. Date and Time Functions

This section describes the functions that can be used to manipulate temporal values. See Section 11.3, “Date and Time Types” for a description of the range of values each date and time type has and the valid formats in which values may be specified.

Here is an example that uses date functions. The following query selects all records with a date_col value from within the last 30 days:

mysql> SELECT something FROM tbl_name
    -> WHERE DATE_SUB(CURDATE(),INTERVAL 30 DAY) <= date_col;

Note that the query also selects records with dates that lie in the future.

Functions that expect date values usually accept datetime values and ignore the time part. Functions that expect time values usually accept datetime values and ignore the date part.

Functions that return the current date or time each are evaluated only once per query at the start of query execution. This means that multiple references to a function such as NOW() within a single query always produce the same result (for our purposes a single query also includes a call to a stored routine or trigger and all sub-routines called by that routine/trigger). This principle also applies to CURDATE(), CURTIME(), UTC_DATE(), UTC_TIME(), UTC_TIMESTAMP(), and to any of their synonyms.

The CURRENT_TIMESTAMP(), CURRENT_TIME(), CURRENT_DATE(), and FROM_UNIXTIME() functions return values in the connection's current time zone, which is available as the value of the time_zone system variable. In addition, UNIX_TIMESTAMP() assumes that its argument is a datetime value in the current time zone. See Section 5.10.8, “MySQL Server Time Zone Support”.

The return value ranges in the following function descriptions apply for complete dates. If a date is a “zero” value or an incomplete date such as '2001-11-00', functions that extract a part of a date may return 0. For example, DAYOFMONTH('2001-11-00') returns 0.

  • ADDDATE(date,INTERVAL expr type) ADDDATE(expr,days)

    When invoked with the INTERVAL form of the second argument, ADDDATE() is a synonym for DATE_ADD(). The related function SUBDATE() is a synonym for DATE_SUB(). For information on the INTERVAL argument, see the discussion for DATE_ADD().

    mysql> SELECT DATE_ADD('1998-01-02', INTERVAL 31 DAY);
            -> '1998-02-02'
    mysql> SELECT ADDDATE('1998-01-02', INTERVAL 31 DAY);
            -> '1998-02-02'
    

    If the days argument is simply an integer value, then MySQL 5.0 treats it as the number of days to be added to expr.

    mysql> SELECT ADDDATE('1998-01-02', 31);
            -> '1998-02-02'
    
  • ADDTIME(expr,expr2)

    ADDTIME() adds expr2 to expr and returns the result. expr is a time or datetime expression, and expr2 is a time expression.

    mysql> SELECT ADDTIME('1997-12-31 23:59:59.999999',
        ->                '1 1:1:1.000002');
            -> '1998-01-02 01:01:01.000001'
    mysql> SELECT ADDTIME('01:00:00.999999', '02:00:00.999998');
            -> '03:00:01.999997'
    
  • CONVERT_TZ(dt,from_tz,to_tz)

    CONVERT_TZ() converts a datetime value dt from time zone given by from_tz to the time zone given by to_tz and returns the resulting value. Time zones may be specified as described in Section 5.10.8, “MySQL Server Time Zone Support”. This function returns NULL if the arguments are invalid.

    If the value falls out of the supported range of the TIMESTAMP type when converted fom from_tz to UTC, no conversion occurs. The TIMESTAMP range is described in Section 11.1.2, “Overview of Date and Time Types”.

    mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','GMT','MET');
            -> '2004-01-01 13:00:00'
    mysql> SELECT CONVERT_TZ('2004-01-01 12:00:00','+00:00','+10:00');
            -> '2004-01-01 22:00:00'
    

    Note: To use named time zones such as 'MET' or 'Europe/Moscow', the time zone tables must be properly set up. See Section 5.10.8, “MySQL Server Time Zone Support” for instructions.

  • CURDATE()

    Returns the current date as a value in 'YYYY-MM-DD' or YYYYMMDD format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT CURDATE();
            -> '1997-12-15'
    mysql> SELECT CURDATE() + 0;
            -> 19971215
    
  • CURRENT_DATE CURRENT_DATE()

    CURRENT_DATE and CURRENT_DATE() are synonyms for CURDATE().

  • CURTIME()

    Returns the current time as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT CURTIME();
            -> '23:50:26'
    mysql> SELECT CURTIME() + 0;
            -> 235026
    
  • CURRENT_TIME, CURRENT_TIME()

    CURRENT_TIME and CURRENT_TIME() are synonyms for CURTIME().

  • CURRENT_TIMESTAMP, CURRENT_TIMESTAMP()

    CURRENT_TIMESTAMP and CURRENT_TIMESTAMP() are synonyms for NOW().

  • DATE(expr)

    Extracts the date part of the date or datetime expression expr.

    mysql> SELECT DATE('2003-12-31 01:02:03');
            -> '2003-12-31'
    
  • DATEDIFF(expr,expr2)

    DATEDIFF() returns the number of days between the start date expr and the end date expr2. expr and expr2 are date or date-and-time expressions. Only the date parts of the values are used in the calculation.

    mysql> SELECT DATEDIFF('1997-12-31 23:59:59','1997-12-30');
            -> 1
    mysql> SELECT DATEDIFF('1997-11-30 23:59:59','1997-12-31');
            -> -31
    
  • DATE_ADD(date,INTERVAL expr type) DATE_SUB(date,INTERVAL expr type)

    These functions perform date arithmetic. date is a DATETIME or DATE value specifying the starting date. expr is an expression specifying the interval value to be added or subtracted from the starting date. expr is a string; it may start with a ‘-’ for negative intervals. type is a keyword indicating how the expression should be interpreted.

    The INTERVAL keyword and the type specifier are not case sensitive.

    The following table shows how the type and expr arguments are related:

    type ValueExpected expr Format
    MICROSECONDMICROSECONDS
    SECONDSECONDS
    MINUTEMINUTES
    HOURHOURS
    DAYDAYS
    WEEKWEEKS
    MONTHMONTHS
    QUARTERQUARTERS
    YEARYEARS
    SECOND_MICROSECOND'SECONDS.MICROSECONDS'
    MINUTE_MICROSECOND'MINUTES.MICROSECONDS'
    MINUTE_SECOND'MINUTES:SECONDS'
    HOUR_MICROSECOND'HOURS.MICROSECONDS'
    HOUR_SECOND'HOURS:MINUTES:SECONDS'
    HOUR_MINUTE'HOURS:MINUTES'
    DAY_MICROSECOND'DAYS.MICROSECONDS'
    DAY_SECOND'DAYS HOURS:MINUTES:SECONDS'
    DAY_MINUTE'DAYS HOURS:MINUTES'
    DAY_HOUR'DAYS HOURS'
    YEAR_MONTH'YEARS-MONTHS'

    The values QUARTER and WEEK are available beginning with MySQL 5.0.0.

    MySQL allows any punctuation delimiter in the expr format. Those shown in the table are the suggested delimiters. If the date argument is a DATE value and your calculations involve only YEAR, MONTH, and DAY parts (that is, no time parts), the result is a DATE value. Otherwise, the result is a DATETIME value.

    INTERVAL expr type is allowed on either side of the + operator if the expression on the other side is a date or datetime value. For the - operator, INTERVAL expr type is allowed only on the right side, because it makes no sense to subtract a date or datetime value from an interval. (See examples below.)

    mysql> SELECT '1997-12-31 23:59:59' + INTERVAL 1 SECOND;
            -> '1998-01-01 00:00:00'
    mysql> SELECT INTERVAL 1 DAY + '1997-12-31';
            -> '1998-01-01'
    mysql> SELECT '1998-01-01' - INTERVAL 1 SECOND;
            -> '1997-12-31 23:59:59'
    mysql> SELECT DATE_ADD('1997-12-31 23:59:59',
        ->                 INTERVAL 1 SECOND);
            -> '1998-01-01 00:00:00'
    mysql> SELECT DATE_ADD('1997-12-31 23:59:59',
        ->                 INTERVAL 1 DAY);
            -> '1998-01-01 23:59:59'
    mysql> SELECT DATE_ADD('1997-12-31 23:59:59',
        ->                 INTERVAL '1:1' MINUTE_SECOND);
            -> '1998-01-01 00:01:00'
    mysql> SELECT DATE_SUB('1998-01-01 00:00:00',
        ->                 INTERVAL '1 1:1:1' DAY_SECOND);
            -> '1997-12-30 22:58:59'
    mysql> SELECT DATE_ADD('1998-01-01 00:00:00',
        ->                 INTERVAL '-1 10' DAY_HOUR);
            -> '1997-12-30 14:00:00'
    mysql> SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY);
            -> '1997-12-02'
    mysql> SELECT DATE_ADD('1992-12-31 23:59:59.000002',
        ->            INTERVAL '1.999999' SECOND_MICROSECOND);
            -> '1993-01-01 00:00:01.000001'
    

    If you specify an interval value that is too short (does not include all the interval parts that would be expected from the type keyword), MySQL assumes that you have left out the leftmost parts of the interval value. For example, if you specify a type of DAY_SECOND, the value of expr is expected to have days, hours, minutes, and seconds parts. If you specify a value like '1:10', MySQL assumes that the days and hours parts are missing and the value represents minutes and seconds. In other words, '1:10' DAY_SECOND is interpreted in such a way that it is equivalent to '1:10' MINUTE_SECOND. This is analogous to the way that MySQL interprets TIME values as representing elapsed time rather than as a time of day.

    If you add to or subtract from a date value something that contains a time part, the result is automatically converted to a datetime value:

    mysql> SELECT DATE_ADD('1999-01-01', INTERVAL 1 DAY);
            -> '1999-01-02'
    mysql> SELECT DATE_ADD('1999-01-01', INTERVAL 1 HOUR);
            -> '1999-01-01 01:00:00'
    

    If you use very badly malformed dates, the result is NULL. If you add MONTH, YEAR_MONTH, or YEAR and the resulting date has a day that is larger than the maximum day for the new month, the day is adjusted to the maximum days in the new month:

    mysql> SELECT DATE_ADD('1998-01-30', INTERVAL 1 MONTH);
            -> '1998-02-28'
    
  • DATE_FORMAT(date,format)

    Formats the date value according to the format string.

    The following specifiers may be used in the format string:

    SpecifierDescription
    %aAbbreviated weekday name (Sun..Sat)
    %bAbbreviated month name (Jan..Dec)
    %cMonth, numeric (0..12)
    %DDay of the month with English suffix (0th, 1st, 2nd, 3rd, ...)
    %dDay of the month, numeric (00..31)
    %eDay of the month, numeric (0..31)
    %fMicroseconds (000000..999999)
    %HHour (00..23)
    %hHour (01..12)
    %IHour (01..12)
    %iMinutes, numeric (00..59)
    %jDay of year (001..366)
    %kHour (0..23)
    %lHour (1..12)
    %MMonth name (January..December)
    %mMonth, numeric (00..12)
    %pAM or PM
    %rTime, 12-hour (hh:mm:ss followed by AM or PM)
    %SSeconds (00..59)
    %sSeconds (00..59)
    %TTime, 24-hour (hh:mm:ss)
    %UWeek (00..53), where Sunday is the first day of the week
    %uWeek (00..53), where Monday is the first day of the week
    %VWeek (01..53), where Sunday is the first day of the week; used with %X
    %vWeek (01..53), where Monday is the first day of the week; used with %x
    %WWeekday name (Sunday..Saturday)
    %wDay of the week (0=Sunday..6=Saturday)
    %XYear for the week where Sunday is the first day of the week, numeric, four digits; used with %V
    %xYear for the week, where Monday is the first day of the week, numeric, four digits; used with %v
    %YYear, numeric, four digits
    %yYear, numeric (two digits)
    %%A literal ‘%’ character

    All other characters are copied to the result without interpretation.

    Note that the ‘%’ character is required before format specifier characters.

    Ranges for the month and day specifiers begin with zero due to the fact that MySQL allows the storing of incomplete dates such as '2004-00-00'.

    mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00', '%W %M %Y');
            -> 'Saturday October 1997'
    mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00', '%H:%i:%s');
            -> '22:23:00'
    mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00',
                              '%D %y %a %d %m %b %j');
            -> '4th 97 Sat 04 10 Oct 277'
    mysql> SELECT DATE_FORMAT('1997-10-04 22:23:00',
                              '%H %k %I %r %T %S %w');
            -> '22 22 10 10:23:00 PM 22:23:00 00 6'
    mysql> SELECT DATE_FORMAT('1999-01-01', '%X %V');
            -> '1998 52'
    
  • DAY(date)

    DAY() is a synonym for DAYOFMONTH().

  • DAYNAME(date)

    Returns the name of the weekday for date.

    mysql> SELECT DAYNAME('1998-02-05');
            -> 'Thursday'
    
  • DAYOFMONTH(date)

    Returns the day of the month for date, in the range 1 to 31.

    mysql> SELECT DAYOFMONTH('1998-02-03');
            -> 3
    
  • DAYOFWEEK(date)

    Returns the weekday index for date (1 = Sunday, 2 = Monday, ..., 7 = Saturday). These index values correspond to the ODBC standard.

    mysql> SELECT DAYOFWEEK('1998-02-03');
            -> 3
    
  • DAYOFYEAR(date)

    Returns the day of the year for date, in the range 1 to 366.

    mysql> SELECT DAYOFYEAR('1998-02-03');
            -> 34
    
  • EXTRACT(type FROM date)

    The EXTRACT() function uses the same kinds of interval type specifiers as DATE_ADD() or DATE_SUB(), but extracts parts from the date rather than performing date arithmetic.

    mysql> SELECT EXTRACT(YEAR FROM '1999-07-02');
           -> 1999
    mysql> SELECT EXTRACT(YEAR_MONTH FROM '1999-07-02 01:02:03');
           -> 199907
    mysql> SELECT EXTRACT(DAY_MINUTE FROM '1999-07-02 01:02:03');
           -> 20102
    mysql> SELECT EXTRACT(MICROSECOND
        ->                FROM '2003-01-02 10:30:00.00123');
            -> 123
    
  • FROM_DAYS(N)

    Given a daynumber N, returns a DATE value.

    mysql> SELECT FROM_DAYS(729669);
            -> '1997-10-07'
    

    Use FROM_DAYS() with caution on old dates. It is not intended for use with values that precede the advent of the Gregorian calendar (1582). See Section 12.6, “What Calendar Is Used By MySQL?”.

  • FROM_UNIXTIME(unix_timestamp) , FROM_UNIXTIME(unix_timestamp,format)

    Returns a representation of the unix_timestamp argument as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context.

    If format is given, the result is formatted according to the format string. format may contain the same specifiers as those listed in the entry for the DATE_FORMAT() function.

    mysql> SELECT FROM_UNIXTIME(875996580);
            -> '1997-10-04 22:23:00'
    mysql> SELECT FROM_UNIXTIME(875996580) + 0;
            -> 19971004222300
    
    mysql> SELECT FROM_UNIXTIME(UNIX_TIMESTAMP(),
        ->                      '%Y %D %M %h:%i:%s %x');
            -> '2003 6th August 06:22:58 2003'
    
  • GET_FORMAT(DATE|TIME|DATETIME, 'EUR'|'USA'|'JIS'|'ISO'|'INTERNAL')

    Returns a format string. This function is useful in combination with the DATE_FORMAT() and the STR_TO_DATE() functions.

    The three possible values for the first argument and the five possible values for the second argument result in 15 possible format strings (for the specifiers used, see the table in the DATE_FORMAT() function description).

    Function CallResult
    GET_FORMAT(DATE,'USA')'%m.%d.%Y'
    GET_FORMAT(DATE,'JIS')'%Y-%m-%d'
    GET_FORMAT(DATE,'ISO')'%Y-%m-%d'
    GET_FORMAT(DATE,'EUR')'%d.%m.%Y'
    GET_FORMAT(DATE,'INTERNAL')'%Y%m%d'
    GET_FORMAT(DATETIME,'USA')'%Y-%m-%d-%H.%i.%s'
    GET_FORMAT(DATETIME,'JIS')'%Y-%m-%d %H:%i:%s'
    GET_FORMAT(DATETIME,'ISO')'%Y-%m-%d %H:%i:%s'
    GET_FORMAT(DATETIME,'EUR')'%Y-%m-%d-%H.%i.%s'
    GET_FORMAT(DATETIME,'INTERNAL')'%Y%m%d%H%i%s'
    GET_FORMAT(TIME,'USA')'%h:%i:%s %p'
    GET_FORMAT(TIME,'JIS')'%H:%i:%s'
    GET_FORMAT(TIME,'ISO')'%H:%i:%s'
    GET_FORMAT(TIME,'EUR')'%H.%i.%S'
    GET_FORMAT(TIME,'INTERNAL')'%H%i%s'

    ISO format is ISO 9075, not ISO 8601.

    TIMESTAMP can also be used, in which case GET_FORMAT() returns the same values as for DATETIME.

    mysql> SELECT DATE_FORMAT('2003-10-03',GET_FORMAT(DATE,'EUR'));
            -> '03.10.2003'
    mysql> SELECT STR_TO_DATE('10.31.2003',GET_FORMAT(DATE,'USA'));
            -> '2003-10-31'
            
    
    
    
    

    See also Section 13.5.3, “SET Syntax”.

  • HOUR(time)

    Returns the hour for time. The range of the return value is 0 to 23 for time-of-day values.

    mysql> SELECT HOUR('10:05:03');
            -> 10
    

    However, the range of TIME values actually is much larger, so HOUR can return values greater than 23.

    mysql> SELECT HOUR('272:59:59');
            -> 272
    
  • LAST_DAY(date)

    Takes a date or datetime value and returns the corresponding value for the last day of the month. Returns NULL if the argument is invalid.

    mysql> SELECT LAST_DAY('2003-02-05');
            -> '2003-02-28'
    mysql> SELECT LAST_DAY('2004-02-05');
            -> '2004-02-29'
    mysql> SELECT LAST_DAY('2004-01-01 01:01:01');
            -> '2004-01-31'
    mysql> SELECT LAST_DAY('2003-03-32');
            -> NULL
    
  • LOCALTIME, LOCALTIME()

    LOCALTIME and LOCALTIME() are synonyms for NOW().

  • LOCALTIMESTAMP, LOCALTIMESTAMP()

    LOCALTIMESTAMP and LOCALTIMESTAMP() are synonyms for NOW().

  • MAKEDATE(year,dayofyear)

    Returns a date, given year and day-of-year values. dayofyear must be greater than 0 or the result is NULL.

    mysql> SELECT MAKEDATE(2001,31), MAKEDATE(2001,32);
            -> '2001-01-31', '2001-02-01'
    mysql> SELECT MAKEDATE(2001,365), MAKEDATE(2004,365);
            -> '2001-12-31', '2004-12-30'
    mysql> SELECT MAKEDATE(2001,0);
            -> NULL
    
  • MAKETIME(hour,minute,second)

    Returns a time value calculated from the hour, minute, and second arguments.

    mysql> SELECT MAKETIME(12,15,30);
            -> '12:15:30'
    
  • MICROSECOND(expr)

    Returns the microseconds from the time or datetime expression expr as a number in the range from 0 to 999999.

    mysql> SELECT MICROSECOND('12:00:00.123456');
            -> 123456
    mysql> SELECT MICROSECOND('1997-12-31 23:59:59.000010');
            -> 10
    
  • MINUTE(time)

    Returns the minute for time, in the range 0 to 59.

    mysql> SELECT MINUTE('98-02-03 10:05:03');
            -> 5
    
  • MONTH(date)

    Returns the month for date, in the range 1 to 12.

    mysql> SELECT MONTH('1998-02-03');
            -> 2
    
  • MONTHNAME(date)

    Returns the full name of the month for date.

    mysql> SELECT MONTHNAME('1998-02-05');
            -> 'February'
    
  • NOW()

    Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT NOW();
            -> '1997-12-15 23:50:26'
    mysql> SELECT NOW() + 0;
            -> 19971215235026
    

    Within a stored routine or trigger, NOW() returns a constant time that indicates the time at which the routine or triggering statement began to execute. This differs from the behavior for SYSDATE().

  • PERIOD_ADD(P,N)

    Adds N months to period P (in the format YYMM or YYYYMM). Returns a value in the format YYYYMM. Note that the period argument P is not a date value.

    mysql> SELECT PERIOD_ADD(9801,2);
            -> 199803
    
  • PERIOD_DIFF(P1,P2)

    Returns the number of months between periods P1 and P2. P1 and P2 should be in the format YYMM or YYYYMM. Note that the period arguments P1 and P2 are not date values.

    mysql> SELECT PERIOD_DIFF(9802,199703);
            -> 11
    
  • QUARTER(date)

    Returns the quarter of the year for date, in the range 1 to 4.

    mysql> SELECT QUARTER('98-04-01');
            -> 2
    
  • SECOND(time)

    Returns the second for time, in the range 0 to 59.

    mysql> SELECT SECOND('10:05:03');
            -> 3
    
  • SEC_TO_TIME(seconds)

    Returns the seconds argument, converted to hours, minutes, and seconds, as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT SEC_TO_TIME(2378);
            -> '00:39:38'
    mysql> SELECT SEC_TO_TIME(2378) + 0;
            -> 3938
    
  • STR_TO_DATE(str,format)

    This is the reverse of the DATE_FORMAT() function. It takes a string str and a format string format. STR_TO_DATE() returns a DATETIME value if the format string contains both date and time parts, or a DATE or TIME value if the string contains only date or time parts.

    The date, time, or datetime values contained in str should be given in the format indicated by format. For the specifiers that can be used in format, see the table in the DATE_FORMAT() function description. All other characters are just taken verbatim, thus not being interpreted. If str contains an illegal date, time, or datetime value, STR_TO_DATE() returns NULL. Starting from MySQL 5.0.3, an illegal value also produces a warning.

    Range checking on the parts of date values is as described in Section 11.3.1, “The DATETIME, DATE, and TIMESTAMP Types”. This means, for example, that a date with a day part larger than the number of days in a month is allowable as long as the day part is in the range from 1 to 31. Also, “zero” dates or dates with part values of 0 are allowed.

    mysql> SELECT STR_TO_DATE('00/00/0000', '%m/%d/%Y');
            -> '0000-00-00'
    mysql> SELECT STR_TO_DATE('04/31/2004', '%m/%d/%Y');
            -> '2004-04-31'
    
  • SUBDATE(date,INTERVAL expr type) SUBDATE(expr,days)

    When invoked with the INTERVAL form of the second argument, SUBDATE() is a synonym for DATE_SUB(). For information on the INTERVAL argument, see the discussion for DATE_ADD().

    mysql> SELECT DATE_SUB('1998-01-02', INTERVAL 31 DAY);
            -> '1997-12-02'
    mysql> SELECT SUBDATE('1998-01-02', INTERVAL 31 DAY);
            -> '1997-12-02'
    

    The second form allows the use of an integer value for days. In such cases, it is reckoned to be the number of days to be subtracted from the date or datetime expression expr.

    mysql> SELECT SUBDATE('1998-01-02 12:00:00', 31);
            -> '1997-12-02 12:00:00'
    

    Note that you cannot use format "%X%V" to convert a year-week string to a date as the combination of a year and week does not uniquely identify a year and month if the week crosses a month boundary. To convert a year-week to a date, then you should also specify the weekday:

    mysql> select str_to_date('200442 Monday', '%X%V %W');
    -> 2004-10-18
    
  • SUBTIME(expr,expr2)

    SUBTIME() subtracts expr2 from expr and returns the result. expr is a time or datetime expression, and expr2 is a time expression.

    mysql> SELECT SUBTIME('1997-12-31 23:59:59.999999','1 1:1:1.000002');
            -> '1997-12-30 22:58:58.999997'
    mysql> SELECT SUBTIME('01:00:00.999999', '02:00:00.999998');
            -> '-00:59:59.999999'
    
  • SYSDATE()

    Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context.

    Within a stored routine or trigger, SYSDATE() returns the time at which it executes, not the time at which the routine or triggering statement began to execute. This differs from the behavior for NOW().

  • TIME(expr)

    Extracts the time part of the time or datetime expression expr and returns it as a string.

    mysql> SELECT TIME('2003-12-31 01:02:03');
            -> '01:02:03'
    mysql> SELECT TIME('2003-12-31 01:02:03.000123');
            -> '01:02:03.000123'
    
  • TIMEDIFF(expr,expr2)

    TIMEDIFF() returns the time between the start time expr and the end time expr2. expr and expr2 are time or date-and-time expressions, but both must be of the same type.

    mysql> SELECT TIMEDIFF('2000:01:01 00:00:00',
        ->                 '2000:01:01 00:00:00.000001');
            -> '-00:00:00.000001'
    mysql> SELECT TIMEDIFF('1997-12-31 23:59:59.000001',
        ->                 '1997-12-30 01:01:01.000002');
            -> '46:58:57.999999'
    
  • TIMESTAMP(expr) , TIMESTAMP(expr,expr2)

    With a single argument, this function returns the date or datetime expression expr as a datetime value. With two arguments, it adds the time expression expr2 to the date or datetime expression expr and returns theresult as a datetime value.

    mysql> SELECT TIMESTAMP('2003-12-31');
            -> '2003-12-31 00:00:00'
    mysql> SELECT TIMESTAMP('2003-12-31 12:00:00','12:00:00');
            -> '2004-01-01 00:00:00'
    
  • TIMESTAMPADD(interval,int_expr,datetime_expr)

    Adds the integer expression int_expr to the date or datetime expression datetime_expr. The unit for int_expr is given by the interval argument, which should be one of the following values: FRAC_SECOND, SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.

    The interval value may be specified using one of keywords as shown, or with a prefix of SQL_TSI_. For example, DAY or SQL_TSI_DAY both are legal.

    mysql> SELECT TIMESTAMPADD(MINUTE,1,'2003-01-02');
            -> '2003-01-02 00:01:00'
    mysql> SELECT TIMESTAMPADD(WEEK,1,'2003-01-02');
            -> '2003-01-09'
    

    TIMESTAMPADD() is available as of MySQL 5.0.0.

  • TIMESTAMPDIFF(interval,datetime_expr1,datetime_expr2)

    Returns the integer difference between the date or datetime expressions datetime_expr1 and datetime_expr2. The unit for the result is given by the interval argument. The legal values for interval are the same as those listed in the description of the TIMESTAMPADD() function.

    mysql> SELECT TIMESTAMPDIFF(MONTH,'2003-02-01','2003-05-01');
            -> 3
    mysql> SELECT TIMESTAMPDIFF(YEAR,'2002-05-01','2001-01-01');
            -> -1
    

    TIMESTAMPDIFF() is available as of MySQL 5.0.0.

  • TIME_FORMAT(time,format)

    This is used like the DATE_FORMAT() function, but the format string may contain only those format specifiers that handle hours, minutes, and seconds. Other specifiers produce a NULL value or 0.

    If the time value contains an hour part that is greater than 23, the %H and %k hour format specifiers produce a value larger than the usual range of 0..23. The other hour format specifiers produce the hour value modulo 12.

    mysql> SELECT TIME_FORMAT('100:00:00', '%H %k %h %I %l');
            -> '100 100 04 04 4'
    
  • TIME_TO_SEC(time)

    Returns the time argument, converted to seconds.

    mysql> SELECT TIME_TO_SEC('22:23:00');
            -> 80580
    mysql> SELECT TIME_TO_SEC('00:39:38');
            -> 2378
    
  • TO_DAYS(date)

    Given a date date, returns a daynumber (the number of days since year 0).

    mysql> SELECT TO_DAYS(950501);
            -> 728779
    mysql> SELECT TO_DAYS('1997-10-07');
            -> 729669
    

    TO_DAYS() is not intended for use with values that precede the advent of the Gregorian calendar (1582), because it does not take into account the days that were lost when the calendar was changed. See Section 12.6, “What Calendar Is Used By MySQL?”.

    Remember that MySQL converts two-digit year values in dates to four-digit form using the rules in Section 11.3, “Date and Time Types”. For example, '1997-10-07' and '97-10-07' are seen as identical dates:

    mysql> SELECT TO_DAYS('1997-10-07'), TO_DAYS('97-10-07');
            -> 729669, 729669
    

    For dates before 1582 (and possibly a later year in other locales), results from this function are not reliable. See Section 12.6, “What Calendar Is Used By MySQL?” for details.

  • UNIX_TIMESTAMP(), UNIX_TIMESTAMP(date)

    If called with no argument, returns a Unix timestamp (seconds since '1970-01-01 00:00:00' GMT) as an unsigned integer. If UNIX_TIMESTAMP() is called with a date argument, it returns the value of the argument as seconds since '1970-01-01 00:00:00' GMT. date may be a DATE string, a DATETIME string, a TIMESTAMP, or a number in the format YYMMDD or YYYYMMDD in local time.

    mysql> SELECT UNIX_TIMESTAMP();
            -> 882226357
    mysql> SELECT UNIX_TIMESTAMP('1997-10-04 22:23:00');
            -> 875996580
    

    When UNIX_TIMESTAMP is used on a TIMESTAMP column, the function returns the internal timestamp value directly, with no implicit “string-to-Unix-timestamp” conversion. If you pass an out-of-range date to UNIX_TIMESTAMP(), it returns 0, but please note that only basic range checking is performed (year from 1970 to 2037, month from 01 to 12, day from 01 from 31).

    If you want to subtract UNIX_TIMESTAMP() columns, you might want to cast the result to signed integers. See Section 12.8, “Cast Functions and Operators”.

  • UTC_DATE, UTC_DATE()

    Returns the current UTC date as a value in 'YYYY-MM-DD' or YYYYMMDD format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT UTC_DATE(), UTC_DATE() + 0;
            -> '2003-08-14', 20030814
    
  • UTC_TIME, UTC_TIME()

    Returns the current UTC time as a value in 'HH:MM:SS' or HHMMSS format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT UTC_TIME(), UTC_TIME() + 0;
            -> '18:07:53', 180753
    
  • UTC_TIMESTAMP, UTC_TIMESTAMP()

    Returns the current UTC date and time as a value in 'YYYY-MM-DD HH:MM:SS' or YYYYMMDDHHMMSS format, depending on whether the function is used in a string or numeric context.

    mysql> SELECT UTC_TIMESTAMP(), UTC_TIMESTAMP() + 0;
            -> '2003-08-14 18:08:04', 20030814180804
    
  • WEEK(date[,mode])

    This function returns the week number for date. The two-argument form of WEEK() allows you to specify whether the week starts on Sunday or Monday and whether the return value should be in the range from 0 to 53 or from 1 to 53. If the mode argument is omitted, the value of the default_week_format system variable is used. See Section 5.3.3, “Server System Variables”.

    The following table describes how the mode argument works:

     First day  
    Modeof weekRangeWeek 1 is the first week...
    0Sunday0-53with a Sunday in this year
    1Monday0-53with more than 3 days this year
    2Sunday1-53with a Sunday in this year
    3Monday1-53with more than 3 days this year
    4Sunday0-53with more than 3 days this year
    5Monday0-53with a Monday in this year
    6Sunday1-53with more than 3 days this year
    7Monday1-53with a Monday in this year
    mysql> SELECT WEEK('1998-02-20');
            -> 7
    mysql> SELECT WEEK('1998-02-20',0);
            -> 7
    mysql> SELECT WEEK('1998-02-20',1);
            -> 8
    mysql> SELECT WEEK('1998-12-31',1);
            -> 53
    

    Note that if a date falls in the last week of the previous year, MySQL returns 0 if you do not use 2, 3, 6, or 7 as the optional mode argument:

    mysql> SELECT YEAR('2000-01-01'), WEEK('2000-01-01',0);
            -> 2000, 0
    

    One might argue that MySQL should return 52 for the WEEK() function, because the given date actually occurs in the 52nd week of 1999. We decided to return 0 instead because we want the function to return “the week number in the given year”. This makes use of the WEEK() function reliable when combined with other functions that extract a date part from a date.

    If you would prefer the result to be evaluated with respect to the year that contains the first day of the week for the given date, you should use 0, 2, 5, or 7 as the optional mode argument.

    mysql> SELECT WEEK('2000-01-01',2);
            -> 52
    

    Alternatively, use the YEARWEEK() function:

    mysql> SELECT YEARWEEK('2000-01-01');
            -> 199952
    mysql> SELECT MID(YEARWEEK('2000-01-01'),5,2);
            -> '52'
    
  • WEEKDAY(date)

    Returns the weekday index for date (0 = Monday, 1 = Tuesday, ... 6 = Sunday).

    mysql> SELECT WEEKDAY('1998-02-03 22:23:00');
            -> 1
    mysql> SELECT WEEKDAY('1997-11-05');
            -> 2
    
  • WEEKOFYEAR(date)

    Returns the calendar week of the date as a number in the range from 1 to 53. It is a compatibility function that is equivalent to WEEK(date,3).

    mysql> SELECT WEEKOFYEAR('1998-02-20');
            -> 8
    
  • YEAR(date)

    Returns the year for date, in the range 1000 to 9999.

    mysql> SELECT YEAR('98-02-03');
            -> 1998
    
  • YEARWEEK(date), YEARWEEK(date,start)

    Returns year and week for a date. The start argument works exactly like the start argument to WEEK(). The year in the result may be different from the year in the date argument for the first and the last week of the year.

    mysql> SELECT YEARWEEK('1987-01-01');
            -> 198653
    

    Note that the week number is different from what the WEEK() function would return (0) for optional arguments 0 or 1, as WEEK() then returns the week in the context of the given year.

12.6. What Calendar Is Used By MySQL?

MySQL uses what is known as a proleptic Gregorian calendar.

Every country that has switched from the Julian to the Gregorian calendar has had to discard at least ten days during the switch. To see how this works, let's look at the month of October 1582, when the first Julian-to-Gregorian switch occurred:

MondayTuesdayWednesdayThursdayFridaySaturdaySunday
1234151617
18192021222324
25262728293031

There are no dates between October 4 and October 15. This discontinuity is called the cutover. Any dates before the cutover are Julian, and any dates following the cutover are Gregorian. Dates during a cutover are nonexistent.

A calendar applied to dates when it wasn't actually in use is called proleptic. Thus, if we assume there was never a cutover and Gregorian rules always rule, we have a proleptic Gregorian calendar. This is what is used by MySQL, as is required by standard SQL. For this reason, dates prior to the cutover stored as MySQL DATE or DATETIME values must be adjusted to compensate for the difference. It is important to realise that the cutover did not occur at the same time in all countries, and that the later it happened, the more days were lost. For example, in Great Britain, it took place in 1752, when Wednesday September 2 was followed by Thursday September 14; Russia remained on the Julian calendar until 1918, losing 13 days in the process, and what is popularly referred to as its “October Revolution” occurred in November according to the Gregorian calendar.

12.7. Full-Text Search Functions

  • MATCH (col1,col2,...) AGAINST (expr [IN BOOLEAN MODE | WITH QUERY EXPANSION])

    MySQL has support for full-text indexing and searching. A full-text index in MySQL is an index of type FULLTEXT. FULLTEXT indexes can be used only with MyISAM tables; they can be created from CHAR, VARCHAR, or TEXT columns as part of a CREATE TABLE statement or added later using ALTER TABLE or CREATE INDEX. For large datasets, it is much faster to load your data into a table that has no FULLTEXT index, and then create the index afterwards, than to load data into a table that has an existing FULLTEXT index.

    Constraints on full-text searching are listed in Section 12.7.4, “Full-Text Restrictions”.

Full-text searching is performed with the MATCH() function.

mysql> CREATE TABLE articles (
    ->   id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,
    ->   title VARCHAR(200),
    ->   body TEXT,
    ->   FULLTEXT (title,body)
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO articles (title,body) VALUES
    -> ('MySQL Tutorial','DBMS stands for DataBase ...'),
    -> ('How To Use MySQL Well','After you went through a ...'),
    -> ('Optimizing MySQL','In this tutorial we will show ...'),
    -> ('1001 MySQL Tricks','1. Never run mysqld as root. 2. ...'),
    -> ('MySQL vs. YourSQL','In the following database comparison ...'),
    -> ('MySQL Security','When configured properly, MySQL ...');
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM articles
    -> WHERE MATCH (title,body) AGAINST ('database');
+----+-------------------+------------------------------------------+
| id | title             | body                                     |
+----+-------------------+------------------------------------------+
|  5 | MySQL vs. YourSQL | In the following database comparison ... |
|  1 | MySQL Tutorial    | DBMS stands for DataBase ...             |
+----+-------------------+------------------------------------------+
2 rows in set (0.00 sec)

The MATCH() function performs a natural language search for a string against a text collection. A collection is a set of one or more columns included in a FULLTEXT index. The search string is given as the argument to AGAINST(). For each row in the table, MATCH() returns a relevance value, that is, a similarity measure between the search string and the text in that row in the columns named in the MATCH() list.

By default, the search is performed in case-insensitive fashion. However, you can perform a case-sensitive full-text search by using a binary collation for the indexed columns. For example, a column that uses the latin1 character set of can be assigned a collation of latin1_bin to make it case sensitive for full-text searches.

When MATCH() is used in a WHERE clause, as in the preceding example, the rows returned are automatically sorted with the highest relevance first. Relevance values are non-negative floating-point numbers. Zero relevance means no similarity. Relevance is computed based on the number of words in the row, the number of unique words in that row, the total number of words in the collection, and the number of documents (rows) that contain a particular word.

For natural-language full-text searches, it is a requirement that the columns named in the MATCH() function be the same columns included in some FULLTEXT index in your table. For the preceding query, note that the columns named in the MATCH() function (title and body) are the same as those named in the definition of the article table's FULLTEXT index. If you wanted to search the title or body separately, you would need to create FULLTEXT indexes for each column.

It is also possible to perform a boolean search or a search with query expansion. These search types are described in Section 12.7.1, “Boolean Full-Text Searches” and Section 12.7.2, “Full-Text Searches with Query Expansion”.

The preceding example is a basic illustration showing how to use the MATCH() function where rows are returned in order of decreasing relevance. The next example shows how to retrieve the relevance values explicitly. Returned rows are not ordered because the SELECT statement includes neither WHERE nor ORDER BY clauses:

mysql> SELECT id, MATCH (title,body) AGAINST ('Tutorial')
    -> FROM articles;
+----+-----------------------------------------+
| id | MATCH (title,body) AGAINST ('Tutorial') |
+----+-----------------------------------------+
|  1 |                        0.65545833110809 |
|  2 |                                       0 |
|  3 |                        0.66266459226608 |
|  4 |                                       0 |
|  5 |                                       0 |
|  6 |                                       0 |
+----+-----------------------------------------+
6 rows in set (0.00 sec)

The following example is more complex. The query returns the relevance values and it also sorts the rows in order of decreasing relevance. To achieve this result, you should specify MATCH() twice: once in the SELECT list and once in the WHERE clause. This causes no additional overhead, because the MySQL optimizer notices that the two MATCH() calls are identical and invokes the full-text search code only once.

mysql> SELECT id, body, MATCH (title,body) AGAINST
    -> ('Security implications of running MySQL as root') AS score
    -> FROM articles WHERE MATCH (title,body) AGAINST
    -> ('Security implications of running MySQL as root');
+----+-------------------------------------+-----------------+
| id | body                                | score           |
+----+-------------------------------------+-----------------+
|  4 | 1. Never run mysqld as root. 2. ... | 1.5219271183014 |
|  6 | When configured properly, MySQL ... | 1.3114095926285 |
+----+-------------------------------------+-----------------+
2 rows in set (0.00 sec)

The MySQL FULLTEXT implementation regards any sequence of true word characters (letters, digits, and underscores) as a word. That sequence may also contain apostrophes ('), but not more than one in a row. This means that aaa'bbb is regarded as one word, but aaa''bbb is regarded as two words. Apostrophes at the beginning or the end of a word are stripped by the FULLTEXT parser; 'aaa'bbb' would be parsed as aaa'bbb.

The FULLTEXT parser determines where words start and end by looking for certain delimiters, for example ' ' (the space character), , (the comma), and . (the period). If words are not separated by delimiters (as in, for example, Chinese), the FULLTEXT parser cannot determine where a word begins or ends. To be able to add words or other indexed terms in such languages to a FULLTEXT index, you must preprocess them so that they are separated by some arbitrary delimiter such as ".

Some words are ignored in full-text searches:

  • Any word that is too short is ignored. The default minimum length of words that are found by full-text searches is four characters.

  • Words in the stopword list are ignored. A stopword is a word such as “the” or “some” that is so common that it is considered to have zero semantic value. There is a built-in stopword list, but it can be overwritten by a user-defined list. See Section 12.7.5, “Fine-Tuning MySQL Full-Text Search”.

The default stopword list is given in Section 12.7.3, “Full-Text Stopwords”. The default minimum word length and stopword list can be changed as described in Section 12.7.5, “Fine-Tuning MySQL Full-Text Search”.

Every correct word in the collection and in the query is weighted according to its significance in the collection or query. This way, a word that is present in many documents has a lower weight (and may even have a zero weight), because it has lower semantic value in this particular collection. Conversely, if the word is rare, it receives a higher weight. The weights of the words are then combined to compute the relevance of the row.

Such a technique works best with large collections (in fact, it was carefully tuned this way). For very small tables, word distribution does not adequately reflect their semantic value, and this model may sometimes produce bizarre results. For example, although the word “MySQL” is present in every row of the articles table, a search for the word produces no results:

mysql> SELECT * FROM articles
    -> WHERE MATCH (title,body) AGAINST ('MySQL');
Empty set (0.00 sec)

The search result is empty because the word “MySQL” is present in at least 50% of the rows. As such, it is effectively treated as a stopword. For large datasets, this is the most desirable behavior — a natural language query should not return every second row from a 1GB table. For small datasets, it may be less desirable.

A word that matches half of the rows in a table is less likely to locate relevant documents. In fact, it most likely finds plenty of irrelevant documents. We all know this happens far too often when we are trying to find something on the Internet with a search engine. It is with this reasoning that rows containing the word are assigned a low semantic value for the particular dataset in which they occur. A given word may exceed the 50% threshold in one dataset but not another.

The 50% threshold has a significant implication when you first try full-text searching to see how it works: If you create a table and insert only one or two rows of text into it, every word in the text occurs in at least 50% of the rows. As a result, no search returns any results. Be sure to insert at least three rows, and preferably many more. Users who need to bypass the 50% limitation can use the boolean search mode; see Section 12.7.1, “Boolean Full-Text Searches”.

12.7.1. Boolean Full-Text Searches

MySQL can also perform boolean full-text searches using the IN BOOLEAN MODE modifier:

mysql> SELECT * FROM articles WHERE MATCH (title,body)
    -> AGAINST ('+MySQL -YourSQL' IN BOOLEAN MODE);
+----+-----------------------+-------------------------------------+
| id | title                 | body                                |
+----+-----------------------+-------------------------------------+
|  1 | MySQL Tutorial        | DBMS stands for DataBase ...        |
|  2 | How To Use MySQL Well | After you went through a ...        |
|  3 | Optimizing MySQL      | In this tutorial we will show ...   |
|  4 | 1001 MySQL Tricks     | 1. Never run mysqld as root. 2. ... |
|  6 | MySQL Security        | When configured properly, MySQL ... |
+----+-----------------------+-------------------------------------+

This query retrieves all the rows that contain the word “MySQL” but that do not contain the word “YourSQL”.

Boolean full-text searches have these characteristics:

  • They do not use the 50% threshold.

  • They do not automatically sort rows in order of decreasing relevance. You can see this from the preceding query result: The row with the highest relevance is the one that contains “MySQL” twice, but it is listed last, not first.

  • They can work even without a FULLTEXT index, although a search executed in this fashion would be quite slow.

  • The minimum and maximum word length full-text parameters apply.

  • The stopword list applies.

The boolean full-text search capability supports the following operators:

  • +

    A leading plus sign indicates that this word must be present in each row that is returned.

  • -

    A leading minus sign indicates that this word must not be present in any of the rows that are returned.

  • (no operator)

    By default (when neither + nor - is specified) the word is optional, but the rows that contain it are rated higher. This mimics the behavior of MATCH() ... AGAINST() without the IN BOOLEAN MODE modifier.

  • > <

    These two operators are used to change a word's contribution to the relevance value that is assigned to a row. The > operator increases the contribution and the < operator decreases it. See the example below.

  • ( )

    Parentheses are used to group words into subexpressions. Parenthesized groups can be nested.

  • ~

    A leading tilde acts as a negation operator, causing the word's contribution to the row's relevance to be negative. This is useful for marking “noise” words. A row containing such a word is rated lower than others, but is not excluded altogether, as it would be with the - operator.

  • *

    The asterisk serves as the truncation operator. Unlike the other operators, it should be appended to the word to be affected.

  • "

    A phrase that is enclosed within double quote (‘"’) characters matches only rows that contain the phrase literally, as it was typed. The full-text engine splits the phrase into words, performs a search in the FULLTEXT index for the words. Prior to MySQL 5.0.3, the engine then performed a substring search for the phrase in the records that were found, so the match must include non-word characters in the phrase. As of MySQL 5.0.3, non-word characters need not be matched exactly: Phrase searching requires only that matches contain exactly the same words as the phrase and in the same order. For example, "test phrase" matches "test, phrase" in MySQL 5.0.3, but not before.

    If the phrase contains no words that are in the index, the result is empty. For example, if all words are either stopwords or shorter than the minimum length of indexed words, the result is empty.

The following examples demonstrate some search strings that use boolean full-text operators:

  • 'apple banana'

    Find rows that contain at least one of the two words.

  • '+apple +juice'

    Find rows that contain both words.

  • '+apple macintosh'

    Find rows that contain the word “apple”, but rank rows higher if they also contain “macintosh”.

  • '+apple -macintosh'

    Find rows that contain the word “apple” but not “macintosh”.

  • '+apple +(>turnover <strudel)'

    Find rows that contain the words “apple” and “turnover”, or “apple” and “strudel” (in any order), but rank “apple turnover” higher than “apple strudel”.

  • 'apple*'

    Find rows that contain words such as “apple”, “apples”, “applesauce”, or “applet”.

  • '"some words"'

    Find rows that contain the exact phrase “some words” (for example, rows that contain “some words of wisdom” but not “some noise words”). Note that the ‘"’ characters that surround the phrase are operator characters that delimit the phrase. They are not the quotes that surround the search string itself.

12.7.2. Full-Text Searches with Query Expansion

Full-text search supports query expansion (and in particular, its variant “blind query expansion”). This is generally useful when a search phrase is too short, which often means that the user is relying on implied knowledge that the full-text search engine usually lacks. For example, a user searching for “database” may really mean that “MySQL”, “Oracle”, “DB2”, and “RDBMS” all are phrases that should match “databases” and should be returned, too. This is implied knowledge.

Blind query expansion (also known as automatic relevance feedback) is enabled by adding WITH QUERY EXPANSION following the search phrase. It works by performing the search twice, where the search phrase for the second search is the original search phrase concatenated with the few top found documents from the first search. Thus, if one of these documents contains the word “databases” and the word “MySQL”, the second search finds the documents that contain the word “MySQL” even if they do not contain the word “database”. The following example shows this difference:

mysql> SELECT * FROM articles
    -> WHERE MATCH (title,body) AGAINST ('database');
+----+-------------------+------------------------------------------+
| id | title             | body                                     |
+----+-------------------+------------------------------------------+
|  5 | MySQL vs. YourSQL | In the following database comparison ... |
|  1 | MySQL Tutorial    | DBMS stands for DataBase ...             |
+----+-------------------+------------------------------------------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM articles
    -> WHERE MATCH (title,body)
    -> AGAINST ('database' WITH QUERY EXPANSION);
+----+-------------------+------------------------------------------+
| id | title             | body                                     |
+----+-------------------+------------------------------------------+
|  1 | MySQL Tutorial    | DBMS stands for DataBase ...             |
|  5 | MySQL vs. YourSQL | In the following database comparison ... |
|  3 | Optimizing MySQL  | In this tutorial we will show ...        |
+----+-------------------+------------------------------------------+
3 rows in set (0.00 sec)

Another example could be searching for books by Georges Simenon about Maigret, when a user is not sure how to spell “Maigret”. A search for “Megre and the reluctant witnesses” finds only “Maigret and the Reluctant Witnesses” without query expansion. A search with query expansion finds all books with the word “Maigret” on the second pass.

Note: Because blind query expansion tends to increase noise significantly by returning non-relevant documents, it is meaningful to use only when a search phrase is rather short.

12.7.3. Full-Text Stopwords

The following table shows the default list of full-text stopwords:

a'sableaboutaboveaccording
accordinglyacrossactuallyafterafterwards
againagainstain'tallallow
allowsalmostalonealongalready
alsoalthoughalwaysamamong
amongstanandanotherany
anybodyanyhowanyoneanythinganyway
anywaysanywhereapartappearappreciate
appropriatearearen'taroundas
asideaskaskingassociatedat
availableawayawfullybebecame
becausebecomebecomesbecomingbeen
beforebeforehandbehindbeingbelieve
belowbesidebesidesbestbetter
betweenbeyondbothbriefbut
byc'monc'scamecan
can'tcannotcantcausecauses
certaincertainlychangesclearlyco
comcomecomesconcerningconsequently
considerconsideringcontaincontainingcontains
correspondingcouldcouldn'tcoursecurrently
definitelydescribeddespitediddidn't
differentdodoesdoesn'tdoing
don'tdonedowndownwardsduring
eacheduegeighteither
elseelsewhereenoughentirelyespecially
etetceveneverevery
everybodyeveryoneeverythingeverywhereex
exactlyexampleexceptfarfew
fifthfirstfivefollowedfollowing
followsforformerformerlyforth
fourfromfurtherfurthermoreget
getsgettinggivengivesgo
goesgoinggonegotgotten
greetingshadhadn'thappenshardly
hashasn'thavehaven'thaving
hehe'shellohelphence
herherehere'shereafterhereby
hereinhereuponhersherselfhi
himhimselfhishitherhopefully
howhowbeithoweveri'di'll
i'mi'veieifignored
immediateininasmuchincindeed
indicateindicatedindicatesinnerinsofar
insteadintoinwardisisn't
itit'dit'llit'sits
itselfjustkeepkeepskept
knowknowsknownlastlately
laterlatterlatterlyleastless
lestletlet'slikeliked
likelylittlelooklookinglooks
ltdmainlymanymaymaybe
memeanmeanwhilemerelymight
moremoreovermostmostlymuch
mustmymyselfnamenamely
ndnearnearlynecessaryneed
needsneitherneverneverthelessnew
nextninenonobodynon
nonenoonenornormallynot
nothingnovelnownowhereobviously
ofoffoftenohok
okayoldononceone
onesonlyontoorother
othersotherwiseoughtourours
ourselvesoutoutsideoveroverall
ownparticularparticularlyperperhaps
placedpleasepluspossiblepresumably
probablyprovidesquequiteqv
ratherrdrereallyreasonably
regardingregardlessregardsrelativelyrespectively
rightsaidsamesawsay
sayingsayssecondsecondlysee
seeingseemseemedseemingseems
seenselfselvessensiblesent
seriousseriouslysevenseveralshall
sheshouldshouldn'tsincesix
sosomesomebodysomehowsomeone
somethingsometimesometimessomewhatsomewhere
soonsorryspecifiedspecifyspecifying
stillsubsuchsupsure
t'staketakentelltends
ththanthankthanksthanx
thatthat'sthatsthetheir
theirsthemthemselvesthenthence
therethere'sthereaftertherebytherefore
thereintheresthereuponthesethey
they'dthey'llthey'rethey'vethink
thirdthisthoroughthoroughlythose
thoughthreethroughthroughoutthru
thustotogethertootook
towardtowardstriedtriestruly
trytryingtwicetwoun
underunfortunatelyunlessunlikelyuntil
untoupuponususe
usedusefulusesusingusually
valuevariousveryviaviz
vswantwantswaswasn't
waywewe'dwe'llwe're
we'vewelcomewellwentwere
weren'twhatwhat'swhateverwhen
whencewheneverwherewhere'swhereafter
whereaswherebywhereinwhereuponwherever
whetherwhichwhilewhitherwho
who'swhoeverwholewhomwhose
whywillwillingwishwith
withinwithoutwon'twonderwould
wouldwouldn'tyesyetyou
you'dyou'llyou'reyou'veyour
yoursyourselfyourselveszero 

12.7.4. Full-Text Restrictions

  • Full-text searches are supported for MyISAM tables only.

  • Full-text searches can be used with most multi-byte character sets. The exception is that for Unicode; the utf8 character set can be used, but not the ucs2 character set.

  • Ideographic languages such as Chinese and Japanese do not have word delimiters. Therefore, the FULLTEXT parser cannot determine where words begin and end in these and other such languages. The implications of this and some workarounds for the problem are described in Section 12.7, “Full-Text Search Functions”.

  • While the use of multiple character sets within a single table is supported, all columns in a FULLTEXT index must use the same character set and collation.

  • The MATCH() column list must match exactly the column list in some FULLTEXT index definition for the table, unless this MATCH() is IN BOOLEAN MODE.

  • The argument to AGAINST() must be a constant string.

12.7.5. Fine-Tuning MySQL Full-Text Search

MySQL's full-text search capability has few user-tunable parameters. You can exert more control over full-text searching behavior if you have a MySQL source distribution because some changes require source code modifications. See Section 2.8, “MySQL Installation Using a Source Distribution”.

Note that full-text search is carefully tuned for the most effectiveness. Modifying the default behavior in most cases can actually decrease it. Do not alter the MySQL sources unless you know what you are doing.

Most full-text variables described below must be set at server startup time. A server restart is required to change them; they cannot be modified while the server is running.

Some variable changes require that you rebuild the FULLTEXT indexes in your tables. Instructions for doing this are given at the end of this section.

  • The minimum and maximum length of words to be indexed is defined by the ft_min_word_len and ft_max_word_len system variables. (See Section 5.3.3, “Server System Variables”.) The default minimum value is four characters; the default maximum depends on the MySQL version in use. If you change either value, you must rebuild your FULLTEXT indexes. For example, if you want three-character words to be searchable, you can set the ft_min_word_len variable by putting the following lines in an option file:

    [mysqld]
    ft_min_word_len=3
    

    Then restart the server and rebuild your FULLTEXT indexes. Also note particularly the remarks regarding myisamchk in the instructions following this list.

  • To override the default stopword list, set the ft_stopword_file system variable. (See Section 5.3.3, “Server System Variables”.) The variable value should be the pathname of the file containing the stopword list, or the empty string to disable stopword filtering. After changing the value of this variable or the contents of the stopword file, rebuild your FULLTEXT indexes.

    The stopword list is free-form, that is, you may use any non-alphanumeric character such as newline, space, or comma to separate stopwords. Exceptions are the underscore character (_) and a single apostrophe (') which are treated as part of a word. The character set of the stopword list is the server's default character set; see Section 10.3.1, “Server Character Set and Collation”.

  • The 50% threshold for natural language searches is determined by the particular weighting scheme chosen. To disable it, look for the following line in myisam/ftdefs.h:

    #define GWS_IN_USE GWS_PROB
    

    Change that line to this:

    #define GWS_IN_USE GWS_FREQ
    

    Then recompile MySQL. There is no need to rebuild the indexes in this case. Note: By doing this you severely decrease MySQL's ability to provide adequate relevance values for the MATCH() function. If you really need to search for such common words, it would be better to search using IN BOOLEAN MODE instead, which does not observe the 50% threshold.

  • To change the operators used for boolean full-text searches, set the ft_boolean_syntax system variable. This variable also can be changed while the server is running, but you must have the SUPER privilege to do so. No rebuilding of indexes is necessary in this case. See Section 5.3.3, “Server System Variables”, which describes the rules governing how to set this variable.

If you modify full-text variables that affect indexing (ft_min_word_len, ft_max_word_len, or ft_stopword_file), or if you change the stopword file itself, you must rebuild your FULLTEXT indexes after making the changes and restarting the server. To rebuild the indexes in this case, it is sufficient to do a QUICK repair operation:

mysql> REPAIR TABLE tbl_name QUICK;

Note that if you use myisamchk to perform an operation that modifies table indexes (such as repair or analyze), the FULLTEXT indexes are rebuilt using the default full-text parameter values for minimum and maximum word length and the stopword file unless you specify otherwise. This can result in queries failing.

The problem occurs because these parameters are known only by the server. They are not stored in MyISAM index files. To avoid the problem if you have modified the minimum or maximum word length or the stopword file in the server, specify the same ft_min_word_len, ft_max_word_len, and ft_stopword_file values to myisamchk that you use for mysqld. For example, if you have set the minimum word length to 3, you can repair a table with myisamchk like this:

shell> myisamchk --recover --ft_min_word_len=3 tbl_name.MYI

To ensure that myisamchk and the server use the same values for full-text parameters, you can place each one in both the [mysqld] and [myisamchk] sections of an option file:

[mysqld]
ft_min_word_len=3

[myisamchk]
ft_min_word_len=3

An alternative to using myisamchk is to use the REPAIR TABLE, ANALYZE TABLE, OPTIMIZE TABLE, or ALTER TABLE. These statements are performed by the server, which knows the proper full-text parameter values to use.

12.8. Cast Functions and Operators

  • BINARY

    The BINARY operator casts the string following it to a binary string. This is an easy way to force a column comparison to be done byte by byte rather than character by character. This causes the comparison to be case sensitive even if the column isn't defined as BINARY or BLOB. BINARY also causes trailing spaces to be significant.

    mysql> SELECT 'a' = 'A';
            -> 1
    mysql> SELECT BINARY 'a' = 'A';
            -> 0
    mysql> SELECT 'a' = 'a ';
            -> 1
    mysql> SELECT BINARY 'a' = 'a ';
            -> 0
    

    BINARY affects the entire comparison; it can be given before either operand with the same result.

    BINARY str is shorthand for CAST(str AS BINARY).

    Note that in some contexts, if you cast an indexed column to BINARY, MySQL is not able to use the index efficiently.

    If you want to compare a BLOB value or other binary string in case-insensitive fashion, you can do so by taking advantage of the fact that binary strings have no character set, and thus no concept of lettercase. To perform a case-insensitive comparison, use the CONVERT() function to convert the string value to a character set that is not case sensitive. The result is a non-binary string, so the LIKE operation is not case sensitive:

    SELECT 'A' LIKE CONVERT(blob_col USING latin1) FROM tbl_name;
    

    To use a different character set, substitute its name for latin1 in the preceding statement.

    CONVERT() can be used more generally for comparing strings that are represented in different character sets.

  • CAST(expr AS type), CONVERT(expr,type) , CONVERT(expr USING transcoding_name)

    The CAST() and CONVERT() functions can be used to take a value of one type and produce a value of another type.

    The type can be one of the following values:

    • BINARY[(N)]

    • CHAR[(N)]

    • DATE

    • DATETIME

    • DECIMAL

    • SIGNED [INTEGER]

    • TIME

    • UNSIGNED [INTEGER]

    BINARY produces a binary string. See the entry for the BINARY operator in this section for a description of how this affects comparisons.

    If the optional length N is given, BINARY[N] causes the cast to use no more than N bytes of the argument. Similarly, CHAR[N] causes the cast to use no more than N characters of the argument.

    The DECIMAL type is available as of MySQL 5.0.8.

    CAST() and CONVERT(... USING ...) are standard SQL syntax. The non-USING form of CONVERT() is ODBC syntax.

    CONVERT() with USING is used to convert data between different character sets. In MySQL, transcoding names are the same as the corresponding character set names. For example, this statement converts the string 'abc' in the server's default character set to the corresponding string in the utf8 character set:

    SELECT CONVERT('abc' USING utf8);
    

The cast functions are useful when you want to create a column with a specific type in a CREATE ... SELECT statement:

CREATE TABLE new_table SELECT CAST('2000-01-01' AS DATE);

The functions also can be useful for sorting ENUM columns in lexical order. Normally sorting of ENUM columns occurs using the internal numeric values. Casting the values to CHAR results in a lexical sort:

SELECT enum_col FROM tbl_name ORDER BY CAST(enum_col AS CHAR);

CAST(str AS BINARY) is the same thing as BINARY str. CAST(expr AS CHAR) treats the expression as a string with the default character set.

CAST() also changes the result if you use it as part of a more complex expression such as CONCAT('Date: ',CAST(NOW() AS DATE)).

You should not use CAST() to extract data in different formats but instead use string functions like LEFT() or EXTRACT(). See Section 12.5, “Date and Time Functions”.

To cast a string to a numeric value in numeric context, you normally do not have to do anything other than to use the string value as though it were a number:

mysql> SELECT 1+'1';
       -> 2

If you use a number in string context, the number automatically is converted to a BINARY string.

mysql> SELECT CONCAT('hello you ',2);
        -> 'hello you 2'

MySQL supports arithmetic with both signed and unsigned 64-bit values. If you are using numeric operators (such as +) and one of the operands is an unsigned integer, the result is unsigned. You can override this by using the SIGNED and UNSIGNED cast operators to cast the operation to a signed or unsigned 64-bit integer, respectively.

mysql> SELECT CAST(1-2 AS UNSIGNED)
        -> 18446744073709551615
mysql> SELECT CAST(CAST(1-2 AS UNSIGNED) AS SIGNED);
        -> -1

Note that if either operand is a floating-point value, the result is a floating-point value and is not affected by the preceding rule. (In this context, DECIMAL column values are regarded as floating-point values.)

mysql> SELECT CAST(1 AS UNSIGNED) - 2.0;
        -> -1.0

If you are using a string in an arithmetic operation, this is converted to a floating-point number.

12.9. Other Functions

12.9.1. Bit Functions

MySQL uses BIGINT (64-bit) arithmetic for bit operations, so these operators have a maximum range of 64 bits.

  • |

    Bitwise OR:

    mysql> SELECT 29 | 15;
            -> 31
    

    The result is an unsigned 64-bit integer.

  • &

    Bitwise AND:

    mysql> SELECT 29 & 15;
            -> 13
    

    The result is an unsigned 64-bit integer.

  • ^

    Bitwise XOR:

    mysql> SELECT 1 ^ 1;
            -> 0
    mysql> SELECT 1 ^ 0;
            -> 1
    mysql> SELECT 11 ^ 3;
            -> 8
    

    The result is an unsigned 64-bit integer.

  • <<

    Shifts a longlong (BIGINT) number to the left.

    mysql> SELECT 1 << 2;
            -> 4
    

    The result is an unsigned 64-bit integer.

  • >>

    Shifts a longlong (BIGINT) number to the right.

    mysql> SELECT 4 >> 2;
            -> 1
    

    The result is an unsigned 64-bit integer.

  • ~

    Invert all bits.

    mysql> SELECT 5 & ~1;
            -> 4
    

    The result is an unsigned 64-bit integer.

  • BIT_COUNT(N)

    Returns the number of bits that are set in the argument N.

    mysql> SELECT BIT_COUNT(29);
            -> 4
    

12.9.2. Encryption Functions

The functions in this section encrypt and decrypt data values. If you want to store results from an encryption function that might contain arbitrary byte values, use a BLOB column rather than a CHAR or VARCHAR column to avoid potential problems with trailing space removal that would change data values.

  • AES_ENCRYPT(str,key_str) , AES_DECRYPT(crypt_str,key_str)

    These functions allow encryption and decryption of data using the official AES (Advanced Encryption Standard) algorithm, previously known as “Rijndael”. Encoding with a 128-bit key length is used, but you can extend it up to 256 bits by modifying the source. We chose 128 bits because it is much faster and it is secure enough for most purposes.

    The input arguments may be any length. If either argument is NULL, the result of this function is also NULL.

    Because AES is a block-level algorithm, padding is used to encode uneven length strings and so the result string length may be calculated as 16 * (trunc(string_length / 16) + 1).

    If AES_DECRYPT() detects invalid data or incorrect padding, it returns NULL. However, it is possible for AES_DECRYPT() to return a non-NULL value (possibly garbage) if the input data or the key is invalid.

    You can use the AES functions to store data in an encrypted form by modifying your queries:

    INSERT INTO t VALUES (1,AES_ENCRYPT('text','password'));
    

    AES_ENCRYPT() and AES_DECRYPT() can be considered the most cryptographically secure encryption functions currently available in MySQL.

  • DECODE(crypt_str,pass_str)

    Decrypts the encrypted string crypt_str using pass_str as the password. crypt_str should be a string returned from ENCODE().

  • ENCODE(str,pass_str)

    Encrypt str using pass_str as the password. To decrypt the result, use DECODE().

    The result is a binary string of the same length as str. If you want to save it in a column, use a BLOB column type.

  • DES_DECRYPT(crypt_str[,key_str])

    Decrypts a string encrypted with DES_ENCRYPT(). On error, this function returns NULL.

    Note that this function works only if MySQL has been configured with SSL support. See Section 5.8.7, “Using Secure Connections”.

    If no key_str argument is given, DES_DECRYPT() examines the first byte of the encrypted string to determine the DES key number that was used to encrypt the original string, and then reads the key from the DES key file to decrypt the message. For this to work, the user must have the SUPER privilege. The key file can be specified with the --des-key-file server option.

    If you pass this function a key_str argument, that string is used as the key for decrypting the message.

    If the crypt_str argument does not appear to be an encrypted string, MySQL returns the given crypt_str.

  • DES_ENCRYPT(str[,(key_num|key_str)])

    Encrypts the string with the given key using the Triple-DES algorithm. On error, this function returns NULL.

    Note that this function works only if MySQL has been configured with SSL support. See Section 5.8.7, “Using Secure Connections”.

    The encryption key to use is chosen based on the second argument to DES_ENCRYPT(), if one was given:

    ArgumentDescription
    No argumentThe first key from the DES key file is used.
    key_numThe given key number (0-9) from the DES key file is used.
    key_strThe given key string is used to encrypt str.

    The key file can be specified with the --des-key-file server option.

    The return string is a binary string where the first character is CHAR(128 | key_num).

    The 128 is added to make it easier to recognize an encrypted key. If you use a string key, key_num is 127.

    The string length for the result is new_len = orig_len + (8-(orig_len % 8))+1.

    Each line in the DES key file has the following format:

    key_num des_key_str
    

    Each key_num must be a number in the range from 0 to 9. Lines in the file may be in any order. des_key_str is the string that is used to encrypt the message. Between the number and the key there should be at least one space. The first key is the default key that is used if you do not specify any key argument to DES_ENCRYPT()

    You can tell MySQL to read new key values from the key file with the FLUSH DES_KEY_FILE statement. This requires the RELOAD privilege.

    One benefit of having a set of default keys is that it gives applications a way to check for the existence of encrypted column values, without giving the end user the right to decrypt those values.

    mysql> SELECT customer_address FROM customer_table 
         > WHERE crypted_credit_card = DES_ENCRYPT('credit_card_number');
    
  • ENCRYPT(str[,salt])

    Encrypt str using the Unix crypt() system call. The salt argument should be a string with at least two characters. If no salt argument is given, a random value is used.

    mysql> SELECT ENCRYPT('hello');
            -> 'VxuFAJXVARROc'
    

    ENCRYPT() ignores all but the first eight characters of str, at least on some systems. This behavior is determined by the implementation of the underlying crypt() system call.

    If crypt() is not available on your system (as is the case with Windows), ENCRYPT() always returns NULL. Because of this, we recommend that you use MD5() or SHA1() instead, because those two functions exist on all platforms.

  • MD5(str)

    Calculates an MD5 128-bit checksum for the string. The value is returned as a binary string of 32 hex digits, or NULL if the argument was NULL. The return value can, for example, be used as a hash key.

    mysql> SELECT MD5('testing');
            -> 'ae2b1fca515949e5d54fb22b8ed95575'
    

    This is the "RSA Data Security, Inc. MD5 Message-Digest Algorithm."

    If you want to convert the value to uppercase, see the description of binary string conversion given in the entry for the BINARY operator in Section 12.8, “Cast Functions and Operators”.

  • OLD_PASSWORD(str)

    OLD_PASSWORD() was added to MySQL when the implementation of PASSWORD() was changed to improve security. OLD_PASSWORD() returns the value of the old (pre-4.1) implementation of PASSWORD(), and is intended to permit you to reset passwords for any pre-4.1 clients that need to connect to your version 5.0 MySQL server without locking them out. See Section 5.7.9, “Password Hashing in MySQL 4.1”.

  • PASSWORD(str)

    Calculates and returns a password string from the plaintext password str, or NULL if the argument was NULL. This is the function that is used for encrypting MySQL passwords for storage in the Password column of the user grant table.

    mysql> SELECT PASSWORD('badpwd');
            -> '*AAB3E285149C0135D51A520E1940DD3263DC008C'
    

    PASSWORD() encryption is one-way (not reversible).

    PASSWORD() does not perform password encryption in the same way that Unix passwords are encrypted. See ENCRYPT().

    Note: The PASSWORD() function is used by the authentication system in MySQL Server; you should not use it in your own applications. For that purpose, use MD5() or SHA1() instead. Also see RFC 2195 for more information about handling passwords and authentication securely in your applications.

  • SHA1(str) SHA(str)

    Calculates an SHA1 160-bit checksum for the string, as described in RFC 3174 (Secure Hash Algorithm). The value is returned as a string of 40 hex digits, or NULL if the argument was NULL. One of the possible uses for this function is as a hash key. You can also use it as a cryptographically safe function for storing passwords.

    mysql> SELECT SHA1('abc');
            -> 'a9993e364706816aba3e25717850c26c9cd0d89d'
    

    SHA1() can be considered a cryptographically more secure equivalent of MD5(). SHA() is synonymous with SHA1().

12.9.3. Information Functions

  • BENCHMARK(count,expr)

    The BENCHMARK() function executes the expression expr repeatedly count times. It may be used to time how quickly MySQL processes the expression. The result value is always 0. The intended use is from within the mysql client, which reports query execution times:

    mysql> SELECT BENCHMARK(1000000,ENCODE('hello','goodbye'));
    +----------------------------------------------+
    | BENCHMARK(1000000,ENCODE('hello','goodbye')) |
    +----------------------------------------------+
    |                                            0 |
    +----------------------------------------------+
    1 row in set (4.74 sec)
    

    The time reported is elapsed time on the client end, not CPU time on the server end. It is advisable to execute BENCHMARK() several times, and to interpret the result with regard to how heavily loaded the server machine is.

  • CHARSET(str)

    Returns the character set of the string argument.

    mysql> SELECT CHARSET('abc');
            -> 'latin1'
    mysql> SELECT CHARSET(CONVERT('abc' USING utf8));
            -> 'utf8'
    mysql> SELECT CHARSET(USER());
            -> 'utf8'
    
  • COERCIBILITY(str)

    Returns the collation coercibility value of the string argument.

    mysql> SELECT COERCIBILITY('abc' COLLATE latin1_swedish_ci);
            -> 0
    mysql> SELECT COERCIBILITY(USER());
            -> 3
    mysql> SELECT COERCIBILITY('abc');
            -> 4
    

    The return values have the following meanings:

    CoercibilityMeaningExample
    0Explicit collationValue with COLLATE clause
    1No collationConcatenation of strings with different collations
    2Implicit collationColumn value
    3System constantUSER() return value
    4CoercibleLiteral string
    5IgnorableNULL or an expression derived from NULL

    Before MySQL 5.0.3, the return values are shown as follows, and functions such as USER() have a coercibility of 2:

    CoercibilityMeaningExample
    0Explicit collationValue with COLLATE clause
    1No collationConcatenation of strings with different collations
    2Implicit collationColumn value
    3CoercibleLiteral string

    Lower values have higher precedence.

  • COLLATION(str)

    Returns the collation for the character set of the string argument.

    mysql> SELECT COLLATION('abc');
            -> 'latin1_swedish_ci'
    mysql> SELECT COLLATION(_utf8'abc');
            -> 'utf8_general_ci'
    
  • CONNECTION_ID()

    Returns the connection ID (thread ID) for the connection. Every connection has its own unique ID.

    mysql> SELECT CONNECTION_ID();
            -> 23786
    
  • CURRENT_USER, CURRENT_USER()

    Returns the username and hostname combination that the current session was authenticated as. This value corresponds to the MySQL account that determines your access privileges. As of MySQL 5.0.10, within a stored routine that is defined with the SQL SECURITY DEFINER characteristic, CURRENT_USER() returns the creator of the routine.

    The value of CURRENT_USER() can differ from the value of USER().

    mysql> SELECT USER();
            -> 'davida@localhost'
    mysql> SELECT * FROM mysql.user;
    ERROR 1044: Access denied for user ''@'localhost' to
    database 'mysql'
    mysql> SELECT CURRENT_USER();
            -> '@localhost'
    

    The example illustrates that although the client specified a username of davida (as indicated by the value of the USER() function), the server authenticated the client using an anonymous user account (as seen by the empty username part of the CURRENT_USER() value). One way this might occur is that there is no account listed in the grant tables for davida.

    The string returned by CURRENT_USER() uses the utf8 character set.

  • DATABASE()

    Returns the default (current) database name using the utf8 character set. Within a stored routine, the default database is the database that the routine is associated with, which is not necessarily the same as the database that is the default in the calling context.

    mysql> SELECT DATABASE();
            -> 'test'
    

    If there is no default database, DATABASE() returns NULL.

  • FOUND_ROWS()

    A SELECT statement may include a LIMIT clause to restrict the number of rows the server returns to the client. In some cases, it is desirable to know how many rows the statement would have returned without the LIMIT, but without running the statement again. To get this row count, include a SQL_CALC_FOUND_ROWS option in the SELECT statement, then invoke FOUND_ROWS() afterward:

    mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name
        -> WHERE id > 100 LIMIT 10;
    mysql> SELECT FOUND_ROWS();
    

    The second SELECT returns a number indicating how many rows the first SELECT would have returned had it been written without the LIMIT clause. (If the preceding SELECT statement does not include the SQL_CALC_FOUND_ROWS option, then FOUND_ROWS() may return a different result when LIMIT is used than when it is not.)

    The row count available through FOUND_ROWS() is transient and not intended to be available past the statement following the SELECT SQL_CALC_FOUND_ROWS statement. If you need to refer to the value later, save it:

    mysql> SELECT SQL_CALC_FOUND_ROWS * FROM ... ;
    mysql> SET @rows = FOUND_ROWS();
    

    If you are using SELECT SQL_CALC_FOUND_ROWS, MySQL must calculate how many rows are in the full result set. However, this is faster than running the query again without LIMIT, because the result set need not be sent to the client.

    SQL_CALC_FOUND_ROWS and FOUND_ROWS() can be useful in situations when you want to restrict the number of rows that a query returns, but also determine the number of rows in the full result set without running the query again. An example is a Web script that presents a paged display containing links to the pages that show other sections of a search result. Using FOUND_ROWS() allows you to determine how many other pages are needed for the rest of the result.

    The use of SQL_CALC_FOUND_ROWS and FOUND_ROWS() is more complex for UNION queries than for simple SELECT statements, because LIMIT may occur at multiple places in a UNION. It may be applied to individual SELECT statements in the UNION, or global to the UNION result as a whole.

    The intent of SQL_CALC_FOUND_ROWS for UNION is that it should return the row count that would be returned without a global LIMIT. The conditions for use of SQL_CALC_FOUND_ROWS with UNION are:

    • The SQL_CALC_FOUND_ROWS keyword must appear in the first SELECT of the UNION.

    • The value of FOUND_ROWS() is exact only if UNION ALL is used. If UNION without ALL is used, duplicate removal occurs and the value of FOUND_ROWS() is only approximate.

    • If no LIMIT is present in the UNION, SQL_CALC_FOUND_ROWS is ignored and returns the number of rows in the temporary table that is created to process the UNION.

  • LAST_INSERT_ID() LAST_INSERT_ID(expr)

    Returns the first automatically generated value that was set for an AUTO_INCREMENT column by the last INSERT or UPDATE query to affect such a column.

    mysql> SELECT LAST_INSERT_ID();
            -> 195
    

    The ID that was generated is maintained in the server on a per-connection basis. This means that the value which the function returns to a given client is the first AUTO_INCREMENT value generated for most recent statement affecting an AUTO_INCREMENT column by that client. This value cannot be affected by other clients, even if they generate AUTO_INCREMENT values of their own. This behavior ensures that you can retrieve your own ID without concern for the activity of other clients, and without the need for locks or transactions.

    The value of LAST_INSERT_ID() is not changed if you update the AUTO_INCREMENT column of a row with a non-“magic” value (that is, a value that is not NULL and not 0).

    Important: If you insert mutliple rows using a single INSERT statement, LAST_INSERT_ID() returns the value generated for the first inserted row only. The reason for this is to make it possible to reproduce easily the same INSERT statement against some other server.

    For example:

    mysql> USE test;
    Database changed
    mysql> CREATE TABLE t (
        ->   id INT AUTO_INCREMENT NOT NULL PRIMARY KEY,
        ->   name VARCHAR(10) NOT NULL
        -> );
    Query OK, 0 rows affected (0.09 sec)
    
    mysql> INSERT INTO t VALUES (NULL, 'Bob');
    Query OK, 1 row affected (0.01 sec)
    
    mysql> SELECT * FROM t;
    +----+------+
    | id | name |
    +----+------+
    |  1 | Bob  |
    +----+------+
    1 row in set (0.01 sec)
    
    mysql> SELECT LAST_INSERT_ID();
    +------------------+
    | LAST_INSERT_ID() |
    +------------------+
    |                1 |
    +------------------+
    1 row in set (0.00 sec)
    
    mysql> INSERT INTO t VALUES
        -> (NULL, 'Mary'), (NULL, 'Jane'), (NULL, 'Lisa');
    Query OK, 3 rows affected (0.00 sec)
    Records: 3  Duplicates: 0  Warnings: 0
    
    mysql> SELECT * FROM t;
    +----+------+
    | id | name |
    +----+------+
    |  1 | Bob  |
    |  2 | Mary |
    |  3 | Jane |
    |  4 | Lisa |
    +----+------+
    4 rows in set (0.01 sec)
    
    mysql> SELECT LAST_INSERT_ID();
    +------------------+
    | LAST_INSERT_ID() |
    +------------------+
    |                2 |
    +------------------+
    1 row in set (0.00 sec)
    

    Although the second query inserted 3 new rows into t, the ID generated for the first of these rows was 2, and it is this value that is returned by LAST_INSERT_ID().

    If you use INSERT IGNORE and the record is ignored, the AUTO_INCREMENT counter is not incremented and LAST_INSERT_ID() returns 0, which reflects that no record was inserted.

    If expr is given as an argument to LAST_INSERT_ID(), the value of the argument is returned by the function and is remembered as the next value to be returned by LAST_INSERT_ID(). This can be used to simulate sequences:

    • Create a table to hold the sequence counter and initialize it:

      mysql> CREATE TABLE sequence (id INT NOT NULL);
      mysql> INSERT INTO sequence VALUES (0);
      
    • Use the table to generate sequence numbers like this:

      mysql> UPDATE sequence SET id=LAST_INSERT_ID(id+1);
      mysql> SELECT LAST_INSERT_ID();
      

      The UPDATE statement increments the sequence counter and causes the next call to LAST_INSERT_ID() to return the updated value. The SELECT statement retrieves that value. The mysql_insert_id() C API function can also be used to get the value. See Section 22.2.3.36, “mysql_insert_id().

    You can generate sequences without calling LAST_INSERT_ID(), but the utility of using the function this way is that the ID value is maintained in the server as the last automatically generated value. It is multi-user safe because multiple clients can issue the UPDATE statement and get their own sequence value with the SELECT statement (or mysql_insert_id()), without affecting or being affected by other clients that generate their own sequence values.

    Note that mysql_insert_id() is only updated after INSERT and UPDATE statements, so you cannot use the C API function to retrieve the value for LAST_INSERT_ID(expr) after executing other SQL statements like SELECT or SET.

  • ROW_COUNT()

    ROW_COUNT() returns the number of rows updated, inserted, or deleted by the preceding statement. This is the same as the row count that the mysql client displays and the value from the mysql_affected_rows() C API function.

    mysql> INSERT INTO t VALUES(1),(2),(3);
    Query OK, 3 rows affected (0.00 sec)
    Records: 3  Duplicates: 0  Warnings: 0
    
    mysql> SELECT ROW_COUNT();
    +-------------+
    | ROW_COUNT() |
    +-------------+
    |           3 |
    +-------------+
    1 row in set (0.00 sec)
    
    mysql> DELETE FROM t WHERE i IN(1,2);
    Query OK, 2 rows affected (0.00 sec)
    
    mysql> SELECT ROW_COUNT();
    +-------------+
    | ROW_COUNT() |
    +-------------+
    |           2 |
    +-------------+
    1 row in set (0.00 sec)
    

    ROW_COUNT() was added in MySQL 5.0.1.

  • SCHEMA()

    This function is a synonym for DATABASE(). It was added in MySQL 5.0.2.

  • SESSION_USER()

    SESSION_USER() is a synonym for USER().

  • SYSTEM_USER()

    SYSTEM_USER() is a synonym for USER().

  • USER()

    Returns the current MySQL username and hostname.

    mysql> SELECT USER();
            -> 'davida@localhost'
    

    The value indicates the username you specified when connecting to the server, and the client host from which you connected. The value can be different than that of CURRENT_USER().

    You can extract only the username part like this:

    mysql> SELECT SUBSTRING_INDEX(USER(),'@',1);
            -> 'davida'
    

    Because USER() returns a value in the utf8 character set, you should also make sure that the '@' string literal is interpreted in that character set:

    mysql> SELECT SUBSTRING_INDEX(USER(),_utf8'@',1);
            -> 'davida'
    
  • VERSION()

    Returns a string that indicates the MySQL server version. The string uses the utf8 character set.

    mysql> SELECT VERSION();
            -> '5.0.16-standard'
    

    Note that if your version string ends with -log this means that logging is enabled.

12.9.4. Miscellaneous Functions

  • DEFAULT(col_name)

    Returns the default value for a table column. Starting with MySQL 5.0.2, an error results if the column has no default value.

    mysql> UPDATE t SET i = DEFAULT(i)+1 WHERE id < 100;
    
  • FORMAT(X,D)

    Formats the number X to a format like '#,###,###.##', rounded to D decimals, and returns the result as a string. If D is 0, the result has no decimal point or fractional part.

    mysql> SELECT FORMAT(12332.123456, 4);
            -> '12,332.1235'
    mysql> SELECT FORMAT(12332.1,4);
            -> '12,332.1000'
    mysql> SELECT FORMAT(12332.2,0);
            -> '12,332'
    
  • GET_LOCK(str,timeout)

    Tries to obtain a lock with a name given by the string str, with a timeout of timeout seconds. Returns 1 if the lock was obtained successfully, 0 if the attempt timed out (for example, because another client has previously locked the name), or NULL if an error occurred (such as running out of memory or the thread was killed with mysqladmin kill). If you have a lock obtained with GET_LOCK(), it is released when you execute RELEASE_LOCK(), execute a new GET_LOCK(), or your connection terminates (either normally or abnormally).

    This function can be used to implement application locks or to simulate record locks. Names are locked on a server-wide basis. If a name has been locked by one client, GET_LOCK() blocks any request by another client for a lock with the same name. This allows clients that agree on a given lock name to use the name to perform cooperative advisory locking. But be aware that it also allows a client that is not among the set of cooperating clients to lock a name, either inadvertently or deliberately, and thus prevent any of the cooperating clients from locking that name. One way to reduce the likelihood of this is to use lock names that are database-specific or application-specific. For example, use lock names of the form db_name.str or app_name.str.

    mysql> SELECT GET_LOCK('lock1',10);
            -> 1
    mysql> SELECT IS_FREE_LOCK('lock2');
            -> 1
    mysql> SELECT GET_LOCK('lock2',10);
            -> 1
    mysql> SELECT RELEASE_LOCK('lock2');
            -> 1
    mysql> SELECT RELEASE_LOCK('lock1');
            -> NULL
    

    Note that the second RELEASE_LOCK() call returns NULL because the lock 'lock1' was automatically released by the second GET_LOCK() call.

  • INET_ATON(expr)

    Given the dotted-quad representation of a network address as a string, returns an integer that represents the numeric value of the address. Addresses may be 4- or 8-byte addresses.

    mysql> SELECT INET_ATON('209.207.224.40');
            -> 3520061480
    

    The generated number is always in network byte order. For the example just shown, the number is calculated as 209×2563 + 207×2562 + 224×256 + 40.

    INET_ATON() also understands short-form IP addresses:

    mysql> SELECT INET_ATON('127.0.0.1'), INET_ATON('127.1');
            -> 2130706433, 2130706433
    

    NOTE: When storing values generated by INET_ATON(), it is recommended that you use an INT UNSIGNED column. If you use a (signed) INT column, then values corresponding to IP addresses for which the first octet is greater than 127 will be truncated to 2147483647 (that is, the value returned by INET_ATON('127.255.255.255')). See Section 11.2, “Numeric Types”.

  • INET_NTOA(expr)

    Given a numeric network address (4 or 8 byte), returns the dotted-quad representation of the address as a string.

    mysql> SELECT INET_NTOA(3520061480);
            -> '209.207.224.40'
    
  • IS_FREE_LOCK(str)

    Checks whether the lock named str is free to use (that is, not locked). Returns 1 if the lock is free (no one is using the lock), 0 if the lock is in use, and NULL on errors (such as incorrect arguments).

  • IS_USED_LOCK(str)

    Checks whether the lock named str is in use (that is, locked). If so, it returns the connection identifier of the client that holds the lock. Otherwise, it returns NULL.

  • MASTER_POS_WAIT(log_name,log_pos[,timeout])

    This function is useful for control of master/slave synchronization. It blocks until the slave has read and applied all updates up to the specified position in the master log. The return value is the number of log events it had to wait for to get to the specified position. The function returns NULL if the slave SQL thread is not started, the slave's master information is not initialized, the arguments are incorrect, or an error occurs. It returns -1 if the timeout has been exceeded. If the slave SQL thread stops while MASTER_POS_WAIT() is waiting, the function returns NULL. If the slave is past the specified position, the function returns immediately.

    If a timeout value is specified, MASTER_POS_WAIT() stops waiting when timeout seconds have elapsed. timeout must be greater than 0; a zero or negative timeout means no timeout.

  • NAME_CONST(name,value)

    Returns the given value. When used to produce a result set column, NAME_CONST() causes the column to have the given name.

    mysql> SELECT NAME_CONST('myname', 14);
    +--------+
    | myname |
    +--------+
    |     14 |
    +--------+
    

    This function was added in MySQL 5.0.12. It is for internal use only. The server uses it when writing statements from stored routines that contain references to local routine variables, as described in Section 17.4, “Binary Logging of Stored Routines and Triggers” You might see this function in the output from mysqlbinlog.

  • RELEASE_LOCK(str)

    Releases the lock named by the string str that was obtained with GET_LOCK(). Returns 1 if the lock was released, 0 if the lock was not established by this thread (in which case the lock is not released), and NULL if the named lock did not exist. The lock does not exist if it was never obtained by a call to GET_LOCK() or if it has previously been released.

    The DO statement is convenient to use with RELEASE_LOCK(). See Section 13.2.2, “DO Syntax”.

  • SLEEP(duration)

    Sleeps (pauses) for the number of seconds given by the duration argument, then returns 0. If SLEEP() is interrupted, it returns 1. The duration may have a fractional part given in microseconds. This function was added in MySQL 5.0.12.

  • UUID()

    Returns a Universal Unique Identifier (UUID) generated according to “DCE 1.1: Remote Procedure Call” (Appendix A) CAE (Common Applications Environment) Specifications published by The Open Group in October 1997 (Document Number C706, http://www.opengroup.org/public/pubs/catalog/c706.htm).

    A UUID is designed as a number that is globally unique in space and time. Two calls to UUID() are expected to generate two different values, even if these calls are performed on two separate computers that are not connected to each other.

    A UUID is a 128-bit number represented by a string of five hexadecimal numbers in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee format:

    • The first three numbers are generated from a timestamp.

    • The fourth number preserves temporal uniqueness in case the timestamp value loses monotonicity (for example, due to daylight saving time).

    • The fifth number is an IEEE 802 node number that provides spatial uniqueness. A random number is substituted if the latter is not available (for example, because the host computer has no Ethernet card, or we do not know how to find the hardware address of an interface on your operating system). In this case, spatial uniqueness cannot be guaranteed. Nevertheless, a collision should have very low probability.

      Currently, the MAC address of an interface is taken into account only on FreeBSD and Linux. On other operating systems, MySQL uses a randomly generated 48-bit number.

    mysql> SELECT UUID();
            -> '6ccd780c-baba-1026-9564-0040f4311e29'
    

    Note that UUID() does not yet work with replication.

  • VALUES(col_name)

    In an INSERT … ON DUPLICATE KEY UPDATE … statement, you can use the VALUES(col_name) function in the UPDATE clause to refer to column values from the INSERT portion of the statement. In other words, VALUES(col_name) in the UPDATE clause refers to the value of col_name that would be inserted, had no duplicate-key conflict occurred. This function is especially useful in multiple-row inserts. The VALUES() function is meaningful only in INSERT ... UPDATE statements and returns NULL otherwise. Section 13.2.4, “INSERT Syntax”.

    mysql> INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6)
        -> ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b);
    

12.10. Functions and Modifiers for Use with GROUP BY Clauses

12.10.1. GROUP BY (Aggregate) Functions

This section describes group (aggregate) functions that operate on sets of values. Unless otherwise stated, group functions ignore NULL values.

If you use an group function in a statement containing no GROUP BY clause, it is equivalent to grouping on all rows.

  • AVG([DISTINCT] expr)

    Returns the average value of expr. The DISTINCT option can be used as of MySQL 5.0.3 to return the averge of the distinct values of expr.

    AVG() returns NULL if there were no matching rows.

    mysql> SELECT student_name, AVG(test_score)
        ->        FROM student
        ->        GROUP BY student_name;
    
  • BIT_AND(expr)

    Returns the bitwise AND of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision.

    This function returns 18446744073709551615 if there were no matching rows. (This is the value of an unsigned BIGINT value with all bits set to 1.)

  • BIT_OR(expr)

    Returns the bitwise OR of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision.

    This function returns 0 if there were no matching rows.

  • BIT_XOR(expr)

    Returns the bitwise XOR of all bits in expr. The calculation is performed with 64-bit (BIGINT) precision.

    This function returns 0 if there were no matching rows.

  • COUNT(expr)

    Returns a count of the number of non-NULL values in the rows retrieved by a SELECT statement.

    COUNT() returns 0 if there were no matching rows.

    mysql> SELECT student.student_name,COUNT(*)
        ->        FROM student,course
        ->        WHERE student.student_id=course.student_id
        ->        GROUP BY student_name;
    
    

    COUNT(*) is somewhat different in that it returns a count of the number of rows retrieved, whether or not they contain NULL values.

    COUNT(*) is optimized to return very quickly if the SELECT retrieves from one table, no other columns are retrieved, and there is no WHERE clause. For example:

    mysql> SELECT COUNT(*) FROM student;
    

    This optimization applies only to MyISAM tables only, because an exact record count is stored for these table types and can be accessed very quickly. For transactional storage engines (InnoDB, BDB), storing an exact row count is more problematic because multiple transactions may be occurring, each of which may affect the count.

  • COUNT(DISTINCT expr,[expr...])

    Returns a count of the number of different non-NULL values.

    COUNT(DISTINCT) returns 0 if there were no matching rows.

    mysql> SELECT COUNT(DISTINCT results) FROM student;
    

    In MySQL, you can obtain the number of distinct expression combinations that do not contain NULL by giving a list of expressions. In standard SQL, you would have to do a concatenation of all expressions inside COUNT(DISTINCT ...).

  • GROUP_CONCAT(expr)

    This function returns a string result with the concatenated non-NULL values from a group. It returns NULL if there are no non-NULL values. The full syntax is as follows:

    GROUP_CONCAT([DISTINCT] expr [,expr ...]
                 [ORDER BY {unsigned_integer | col_name | expr}
                     [ASC | DESC] [,col_name ...]]
                 [SEPARATOR str_val])
    
    mysql> SELECT student_name,
        ->     GROUP_CONCAT(test_score)
        ->     FROM student
        ->     GROUP BY student_name;
    

    Or:

    mysql> SELECT student_name,
        ->     GROUP_CONCAT(DISTINCT test_score
        ->               ORDER BY test_score DESC SEPARATOR ' ')
        ->     FROM student
        ->     GROUP BY student_name;
    

    In MySQL, you can get the concatenated values of expression combinations. You can eliminate duplicate values by using DISTINCT. If you want to sort values in the result, you should use ORDER BY clause. To sort in reverse order, add the DESC (descending) keyword to the name of the column you are sorting by in the ORDER BY clause. The default is ascending order; this may be specified explicitly using the ASC keyword. SEPARATOR is followed by the string value that should be inserted between values of result. The default is a comma (‘,’). You can remove the separator altogether by specifying SEPARATOR ''.

    You can set a maximum allowed length with the group_concat_max_len system variable. The syntax to do this at runtime is as follows, where val is an unsigned integer:

    SET [SESSION | GLOBAL] group_concat_max_len = val;
    

    If a maximum length has been set, the result is truncated to this maximum length.

  • MIN([DISTINCT] expr), MAX([DISTINCT] expr)

    Returns the minimum or maximum value of expr. MIN() and MAX() may take a string argument; in such cases they return the minimum or maximum string value. See Section 7.4.5, “How MySQL Uses Indexes”. The DISTINCT keyword can be used to find the minimum or maximum of the distinct values of expr, however, this produces the same result as omitting DISTINCT.

    MIN() and MAX() return NULL if there were no matching rows.

    mysql> SELECT student_name, MIN(test_score), MAX(test_score)
        ->        FROM student
        ->        GROUP BY student_name;
    

    For MIN(), MAX(), and other aggregate functions, MySQL currently compares ENUM and SET columns by their string value rather than by the string's relative position in the set. This differs from how ORDER BY compares them. This is expected to be rectified in a future MySQL release.

  • STD(expr) STDDEV(expr)

    Returns the population standard deviation of expr. This is an extension to standard SQL. The STDDEV() form of this function is provided for compatibility with Oracle. As of MySQL 5.0.3, the standard SQL function STDDEV_POP() can be used instead.

    These functions return NULL if there were no matching rows.

  • STDDEV_POP(expr)

    Returns the population standard deviation of expr (the square root of VAR_POP()). This function was added in MySQL 5.0.3. Before 5.0.3, you can use STD() or STDDEV(), which are equivalent but not standard SQL.

    STDDEV_POP() returns NULL if there were no matching rows.

  • STDDEV_SAMP(expr)

    Returns the sample standard deviation of expr (the square root of VAR_SAMP(). This function was added in MySQL 5.0.3.

    STDDEV_SAMP() returns NULL if there were no matching rows.

  • SUM([DISTINCT] expr)

    Returns the sum of expr. If the return set has no rows, SUM() returns NULL. The DISTINCT keyword can be used in MySQL 5.0 to sum only the distinct values of expr.

    SUM() returns NULL if there were no matching rows.

  • VAR_POP(expr)

    Returns the population standard variance of expr. It considers rows as the whole population, not as a sample, so it has the number of rows as the denominator. This function was added in MySQL 5.0.3. Before 5.0.3, you can use VARIANCE(), which is equivalent but is not standard SQL.

    VAR_POP() returns NULL if there were no matching rows.

  • VAR_SAMP(expr)

    Returns the sample variance of expr. That is, the denominator is the number of rows minus one. This function was added in MySQL 5.0.3.

    VAR_SAMP() returns NULL if there were no matching rows.

  • VARIANCE(expr)

    Returns the population standard variance of expr. This is an extension to standard SQL. As of MySQL 5.0.3, the standard SQL function VAR_POP() can be used instead.

    VARIANCE() returns NULL if there were no matching rows.

12.10.2. GROUP BY Modifiers

The GROUP BY clause allows a WITH ROLLUP modifier that causes extra rows to be added to the summary output. These rows represent higher-level (or super-aggregate) summary operations. ROLLUP thus allows you to answer questions at multiple levels of analysis with a single query. It can be used, for example, to provide support for OLAP (Online Analytical Processing) operations.

Suppose that a table named sales has year, country, product, and profit columns for recording sales profitability:

CREATE TABLE sales
(
    year    INT NOT NULL,
    country VARCHAR(20) NOT NULL,
    product VARCHAR(32) NOT NULL,
    profit  INT
);

The table's contents can be summarized per year with a simple GROUP BY like this:

mysql> SELECT year, SUM(profit) FROM sales GROUP BY year;
+------+-------------+
| year | SUM(profit) |
+------+-------------+
| 2000 |        4525 |
| 2001 |        3010 |
+------+-------------+

This output shows the total profit for each year, but if you also want to determine the total profit summed over all years, you must add up the individual values yourself or run an additional query.

Or you can use ROLLUP, which provides both levels of analysis with a single query. Adding a WITH ROLLUP modifier to the GROUP BY clause causes the query to produce another row that shows the grand total over all year values:

mysql> SELECT year, SUM(profit) FROM sales GROUP BY year WITH ROLLUP;
+------+-------------+
| year | SUM(profit) |
+------+-------------+
| 2000 |        4525 |
| 2001 |        3010 |
| NULL |        7535 |
+------+-------------+

The grand total super-aggregate line is identified by the value NULL in the year column.

ROLLUP has a more complex effect when there are multiple GROUP BY columns. In this case, each time there is a “break” (change in value) in any but the last grouping column, the query produces an extra super-aggregate summary row.

For example, without ROLLUP, a summary on the sales table based on year, country, and product might look like this:

mysql> SELECT year, country, product, SUM(profit)
    -> FROM sales
    -> GROUP BY year, country, product;
+------+---------+------------+-------------+
| year | country | product    | SUM(profit) |
+------+---------+------------+-------------+
| 2000 | Finland | Computer   |        1500 |
| 2000 | Finland | Phone      |         100 |
| 2000 | India   | Calculator |         150 |
| 2000 | India   | Computer   |        1200 |
| 2000 | USA     | Calculator |          75 |
| 2000 | USA     | Computer   |        1500 |
| 2001 | Finland | Phone      |          10 |
| 2001 | USA     | Calculator |          50 |
| 2001 | USA     | Computer   |        2700 |
| 2001 | USA     | TV         |         250 |
+------+---------+------------+-------------+

The output indicates summary values only at the year/country/product level of analysis. When ROLLUP is added, the query produces several extra rows:

mysql> SELECT year, country, product, SUM(profit)
    -> FROM sales
    -> GROUP BY year, country, product WITH ROLLUP;
+------+---------+------------+-------------+
| year | country | product    | SUM(profit) |
+------+---------+------------+-------------+
| 2000 | Finland | Computer   |        1500 |
| 2000 | Finland | Phone      |         100 |
| 2000 | Finland | NULL       |        1600 |
| 2000 | India   | Calculator |         150 |
| 2000 | India   | Computer   |        1200 |
| 2000 | India   | NULL       |        1350 |
| 2000 | USA     | Calculator |          75 |
| 2000 | USA     | Computer   |        1500 |
| 2000 | USA     | NULL       |        1575 |
| 2000 | NULL    | NULL       |        4525 |
| 2001 | Finland | Phone      |          10 |
| 2001 | Finland | NULL       |          10 |
| 2001 | USA     | Calculator |          50 |
| 2001 | USA     | Computer   |        2700 |
| 2001 | USA     | TV         |         250 |
| 2001 | USA     | NULL       |        3000 |
| 2001 | NULL    | NULL       |        3010 |
| NULL | NULL    | NULL       |        7535 |
+------+---------+------------+-------------+

For this query, adding ROLLUP causes the output to include summary information at four levels of analysis, not just one. Here's how to interpret the ROLLUP output:

  • Following each set of product rows for a given year and country, an extra summary row is produced showing the total for all products. These rows have the product column set to NULL.

  • Following each set of rows for a given year, an extra summary row is produced showing the total for all countries and products. These rows have the country and products columns set to NULL.

  • Finally, following all other rows, an extra summary row is produced showing the grand total for all years, countries, and products. This row has the year, country, and products columns set to NULL.

Other Considerations When using ROLLUP

The following items list some behaviors specific to the MySQL implementation of ROLLUP:

When you use ROLLUP, you cannot also use an ORDER BY clause to sort the results. In other words, ROLLUP and ORDER BY are mutually exclusive. However, you still have some control over sort order. GROUP BY in MySQL sorts results, and you can use explicit ASC and DESC keywords with columns named in the GROUP BY list to specify sort order for individual columns. (The higher-level summary rows added by ROLLUP still appear after the rows from which they are calculated, regardless of the sort order.)

LIMIT can be used to restrict the number of rows returned to the client. LIMIT is applied after ROLLUP, so the limit applies against the extra rows added by ROLLUP. For example:

mysql> SELECT year, country, product, SUM(profit)
    -> FROM sales
    -> GROUP BY year, country, product WITH ROLLUP
    -> LIMIT 5;
+------+---------+------------+-------------+
| year | country | product    | SUM(profit) |
+------+---------+------------+-------------+
| 2000 | Finland | Computer   |        1500 |
| 2000 | Finland | Phone      |         100 |
| 2000 | Finland | NULL       |        1600 |
| 2000 | India   | Calculator |         150 |
| 2000 | India   | Computer   |        1200 |
+------+---------+------------+-------------+

Using LIMIT with ROLLUP may produce results that are more difficult to interpret, because you have less context for understanding the super-aggregate rows.

The NULL indicators in each super-aggregate row are produced when the row is sent to the client. The server looks at the columns named in the GROUP BY clause following the leftmost one that has changed value. For any column in the result set with a name that is a lexical match to any of those names, its value is set to NULL. (If you specify grouping columns by column number, the server identifies which columns to set to NULL by number.)

Because the NULL values in the super-aggregate rows are placed into the result set at such a late stage in query processing, you cannot test them as NULL values within the query itself. For example, you cannot add HAVING product IS NULL to the query to eliminate from the output all but the super-aggregate rows.

On the other hand, the NULL values do appear as NULL on the client side and can be tested as such using any MySQL client programming interface.

12.10.3. GROUP BY with Hidden Fields

MySQL extends the use of GROUP BY so that you can use columns or calculations in the SELECT list that do not appear in the GROUP BY clause. This stands for “any possible value for this group”. You can use this to get better performance by avoiding sorting and grouping on unnecessary items. For example, you do not need to group on customer.name in the following query:

mysql> SELECT order.custid, customer.name, MAX(payments)
    ->        FROM order,customer
    ->        WHERE order.custid = customer.custid
    ->        GROUP BY order.custid;

In standard SQL, you would have to add customer.name to the GROUP BY clause. In MySQL, the name is redundant if you do not run in ANSI mode.

Do not use this feature if the columns you omit from the GROUP BY part are not unique in the group! You get unpredictable results.

In some cases, you can use MIN() and MAX() to obtain a specific column value even if it isn't unique. The following gives the value of column from the row containing the smallest value in the sort column:

SUBSTR(MIN(CONCAT(RPAD(sort,6,' '),column)),7)

See Section 3.6.4, “The Rows Holding the Group-wise Maximum of a Certain Field”.

Note that if you are trying to follow standard SQL, you can't use expressions in GROUP BY or ORDER BY clauses. You can work around this limitation by using an alias for the expression:

mysql> SELECT id,FLOOR(value/100) AS val 
    ->     FROM tbl_name
    ->     GROUP BY id, val ORDER BY val;

However, MySQL allows you to use expressions in GROUP BY and ORDER BY clauses. For example:

mysql> SELECT id, FLOOR(value/100) FROM tbl_name ORDER BY RAND();