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Auszug aus dem off. MySQL Handbuch! (z.B. auf dt. Kapitel 7.3)
A select_expression or where_definition in a SQL
statement can consist of any expression using the functions described below.
An expression that contains NULL always produces a NULL
value unless otherwise indicated in the documentation for the operators and
functions involved in the expression.
NOTE: 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. Spaces around arguments are permitted, though.
You can force MySQL to accept spaces after the function name by starting mysqld
with --ansi or using the CLIENT_IGNORE_SPACE to mysql_connect(),
but in this case all function names will become reserved words. See section
1.4.3 Running MySQL in ANSI Mode.
For the sake of brevity, examples display the output from the mysql
program in abbreviated form. So this:
mysql> select MOD(29,9);
1 rows in set (0.00 sec)
+-----------+
| mod(29,9) |
+-----------+
| 2 |
+-----------+
is displayed like this:
mysql> select MOD(29,9);
-> 2
( ... )
Use parenthesis to force the order of evaluation in an expression. For example:
mysql> select 1+2*3;
-> 7
mysql> select (1+2)*3;
-> 9
Comparison operations result in a value of 1 (TRUE), 0
(FALSE), or NULL. These functions work for both numbers and strings.
Strings are automatically converted to numbers and numbers to strings as needed
(as in Perl).
MySQL performs comparisons using the following rules:
- If one or both arguments are
NULL, the result of the comparison
is NULL, except for the <=> 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.
- In all other cases, the arguments are compared as floating-point (real)
numbers.
By default, string comparisons are done in case-independent fashion using
the current character set (ISO-8859-1 Latin1 by default, which also works excellently
for English).
The examples below 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
=
- 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
<>
-
!=
- 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
<=>
- Null safe equal:
mysql> select 1 <=> 1, NULL <=> NULL, 1 <=> NULL;
-> 1 1 0
IS NULL
-
IS NOT NULL
- Test whether or not 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
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. The first argument (expr) determines how the
comparison is performed as follows:
- If
expr is a TIMESTAMP, DATE,
or DATETIME column, MIN() and MAX()
are formatted to the same format if they are constants.
- If
expr is a case-insensitive string expression, a case-insensitive
string comparison is done.
- If
expr is a case-sensitive string expression, a case-sensitive
string comparison is done.
- If
expr is an integer expression, an integer comparison
is done.
- Otherwise, a floating-point (real) comparison is done.
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 IN (value,...)
- Returns
1 if expr is any of the values in the
IN list, else returns 0. If all values are constants,
then all values are evaluated according to the type of expr and
sorted. The search for the item is then done using a binary search. This means
IN is very quick if the IN value list consists entirely
of constants. If expr is a case-sensitive string expression,
the string comparison is performed in case-sensitive fashion:
mysql> select 2 IN (0,3,5,'wefwf');
-> 0
mysql> select 'wefwf' IN (0,3,5,'wefwf');
-> 1
expr NOT IN (value,...)
- 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
Note that a comparison of NULL values using = will
always be false!
COALESCE(list)
- Returns first non-
NULL element in list:
mysql> select COALESCE(NULL,1);
-> 1
mysql> select COALESCE(NULL,NULL,NULL);
-> NULL
INTERVAL(N,N1,N2,N3,...)
- Returns
0 if N < N1, 1
if N < N2 and so on. 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
If you are comparing case sensitive string with any of the standard operators
(=, <>..., but not LIKE) end
space will be ignored.
mysql> select "a" ="A ";
-> 1
All logical functions return 1 (TRUE), 0 (FALSE)
or NULL (unknown, which is in most cases the same as FALSE):
NOT
-
!
- Logical NOT. Returns
1 if the argument is 0,
otherwise returns 0. Exception: NOT NULL returns
NULL:
mysql> select NOT 1;
-> 0
mysql> select NOT NULL;
-> NULL
mysql> select ! (1+1);
-> 0
mysql> select ! 1+1;
-> 1
The last example returns 1 because the expression evaluates the
same way as (!1)+1.
OR
-
||
- Logical OR. Returns
1 if either argument is not 0
and not NULL:
mysql> select 1 || 0;
-> 1
mysql> select 0 || 0;
-> 0
mysql> select 1 || NULL;
-> 1
AND
-
&&
- Logical AND. Returns
0 if either argument is 0
or NULL, otherwise returns 1:
mysql> select 1 && NULL;
-> 0
mysql> select 1 && 0;
-> 0
IFNULL(expr1,expr2)
- If
expr1 is
not NULL, IFNULL() returns expr1, else
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'
NULLIF(expr1,expr2)
- If
expr1 = expr2 is true, return NULL else return
expr1. This is the same as CASE WHEN x = y THEN NULL ELSE
x END:
mysql> select NULLIF(1,1);
-> NULL
mysql> select NULLIF(1,2);
-> 1
Note that expr1 is evaluated twice in MySQL if the arguments
are equal.
IF(expr1,expr2,expr3)
- If
expr1 is TRUE (expr1 <> 0 and expr1
<> NULL) then IF() returns expr2,
else 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'
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 above, 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 in MySQL Version 3.23 as follows:
| Expression |
Return value |
| expr2 or expr3 returns string |
string |
| expr2 or expr3 returns a floating-point value |
floating-point |
| expr2 or expr3 returns an integer |
integer |
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, which is true.
If there was no matching result value, then the result after ELSE
is returned. If there is no ELSE part then NULL
is returned:
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 type of the return value (INTEGER, DOUBLE or
STRING) is the same as the type of the first returned value (the
expression after the first THEN).
String-valued functions return NULL if the length of the result
would be greater than the max_allowed_packet server parameter.
See section 5.5.2 Tuning Server Parameters.
For functions that operate on string positions, the first position is numbered
1.
ASCII(str)
- Returns the ASCII code value of the leftmost character
of the string
str. Returns 0 if str
is the empty string. Returns NULL if str is NULL:
mysql> select ASCII('2');
-> 50
mysql> select ASCII(2);
-> 50
mysql> select ASCII('dx');
-> 100
See also the ORD() function.
ORD(str)
- If the leftmost character of the string str is a multi-byte character,
returns the code of multi-byte character by returning the ASCII code value
of the character in the format of:
((first byte ASCII code)*256+(second
byte ASCII code))[*256+third byte ASCII code...]. If the leftmost character
is not a multi-byte character, returns the same value as the like ASCII()
function does:
mysql> select ORD('2');
-> 50
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'
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'
OCT(N)
- Returns a string representation of the octal value of
N, where
N is a longlong number. This is equivalent to CONV(N,10,8).
Returns NULL if N is NULL:
mysql> select OCT(12);
-> '14'
HEX(N)
- 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). Returns NULL if N
is NULL:
mysql> select HEX(255);
-> 'FF'
CHAR(N,...)
-
CHAR() interprets the arguments as integers and returns a
string consisting of the characters given by the ASCII 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'
CONCAT(str1,str2,...)
- Returns the string that results from concatenating the arguments. Returns
NULL if any argument is NULL. May have more than
2 arguments. A numeric argument is converted to the equivalent string form:
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 can be a string as well as the rest of
the arguments. If the separator is NULL, the result will be NULL.
The function will skip any NULLs and empty strings, after the
separator argument. The separator will be added between the strings to be
concatenated:
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'
LENGTH(str)
-
OCTET_LENGTH(str)
-
CHAR_LENGTH(str)
-
CHARACTER_LENGTH(str)
- Returns the length of the string
str:
mysql> select LENGTH('text');
-> 4
mysql> select OCTET_LENGTH('text');
-> 4
Note that for CHAR_LENGTH(), multi-byte characters are only counted
once.
LOCATE(substr,str)
-
POSITION(substr IN str)
- Returns the position of the first occurrence of substring
substr
in string str. Returns 0 if substr
is not in str:
mysql> select LOCATE('bar', 'foobarbar');
-> 4
mysql> select LOCATE('xbar', 'foobar');
-> 0
This function is multi-byte safe.
LOCATE(substr,str,pos)
- 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',5);
-> 7
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 arguments are swapped:
mysql> select INSTR('foobarbar', 'bar');
-> 4
mysql> select INSTR('xbar', 'foobar');
-> 0
This function is multi-byte safe.
LPAD(str,len,padstr)
- Returns the string
str, left-padded with the string padstr
until str is len characters long. If str
is longer than len' then it will be shortened to len
characters.
mysql> select LPAD('hi',4,'??');
-> '??hi'
RPAD(str,len,padstr)
- Returns the string
str, right-padded with the string padstr
until str is len characters long. If str
is longer than len' then it will be shortened to len
characters.
mysql> select RPAD('hi',5,'?');
-> 'hi???'
LEFT(str,len)
- Returns the leftmost
len characters from the string str:
mysql> select LEFT('foobarbar', 5);
-> 'fooba'
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.
SUBSTRING(str,pos,len)
-
SUBSTRING(str FROM pos FOR len)
-
MID(str,pos,len)
- Returns a substring
len characters long from string str,
starting at position pos. The variant form that uses FROM
is ANSI SQL92 syntax:
mysql> select SUBSTRING('Quadratically',5,6);
-> 'ratica'
This function is multi-byte safe.
SUBSTRING(str,pos)
-
SUBSTRING(str FROM pos)
- Returns a substring from string
str starting at position pos:
mysql> select SUBSTRING('Quadratically',5);
-> 'ratically'
mysql> select SUBSTRING('foobarbar' FROM 4);
-> 'barbar'
This function is multi-byte safe.
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:
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.
LTRIM(str)
- Returns the string
str with leading space characters removed:
mysql> select LTRIM(' barbar');
-> 'barbar'
RTRIM(str)
- Returns the string
str with trailing space characters removed:
mysql> select RTRIM('barbar ');
-> 'barbar'
This function is multi-byte safe.
TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)
- Returns the string
str with all remstr prefixes
and/or suffixes removed. If none of the specifiers BOTH, LEADING
or TRAILING are given, BOTH is assumed. If remstr
is 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.
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 4 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-alphanumeric characters are ignored
in the given string. All international alpha characters outside the A-Z range
are treated as vowels:
mysql> select SOUNDEX('Hello');
-> 'H400'
mysql> select SOUNDEX('Quadratically');
-> 'Q36324'
SPACE(N)
- Returns a string consisting of
N space characters:
mysql> select SPACE(6);
-> ' '
REPLACE(str,from_str,to_str)
- Returns the string
str with all all occurrences of the string
from_str replaced by the string to_str:
mysql> select REPLACE('www.mysql.com', 'w', 'Ww');
-> 'WwWwWw.mysql.com'
This function is multi-byte safe.
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'
REVERSE(str)
- Returns the string
str with the order of the characters reversed:
mysql> select REVERSE('abc');
-> 'cba'
This function is multi-byte safe.
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:
mysql> select INSERT('Quadratic', 3, 4, 'What');
-> 'QuWhattic'
This function is multi-byte safe.
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'
FIELD(str,str1,str2,str3,...)
- Returns the index of
str in the str1, str2,
str3, ... list. Returns 0 if str
is not found. 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
1 to N if the string str
is in the 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
will not work properly if the first argument contains a `,':
mysql> SELECT FIND_IN_SET('b','a,b,c,d');
-> 2
MAKE_SET(bits,str1,str2,...)
- Returns a set (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, etc.
NULL strings 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(0,'a','b','c');
-> ''
EXPORT_SET(bits,on,off,[separator,[number_of_bits]])
- Returns a string where for every bit set in 'bit', you get an 'on' string
and for every reset bit you get an 'off' string. Each string is separated
with 'separator' (default ',') and only 'number_of_bits' (default 64) of 'bits'
is used:
mysql> select EXPORT_SET(5,'Y','N',',',4)
-> Y,N,Y,N
LCASE(str)
-
LOWER(str)
- Returns the string
str with all characters changed to lowercase
according to the current character set mapping (the default is ISO-8859-1
Latin1):
mysql> select LCASE('QUADRATICALLY');
-> 'quadratically'
This function is multi-byte safe.
UCASE(str)
-
UPPER(str)
- Returns the string
str with all characters changed to uppercase
according to the current character set mapping (the default is ISO-8859-1
Latin1):
mysql> select UCASE('Hej');
-> 'HEJ'
This function is multi-byte safe.
LOAD_FILE(file_name)
- Reads the file and returns the file contents as a string. The file must
be 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 be smaller than
max_allowed_packet. If the file doesn't
exist or can't be read due to one of the above reasons, the function returns
NULL:
mysql> UPDATE table_name
SET blob_column=LOAD_FILE("/tmp/picture")
WHERE id=1;
If you are not using MySQL Version 3.23, you have to do the reading of the
file inside your application and create an INSERT statement to
update the database with the file information. One way to do this, if you are
using the MySQL++ library, can be found at http://www.mysql.com/documentation/mysql++/mysql++-examples.html.
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, pass it as the argument
to CONCAT().
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 only affects 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). With
LIKE you can use the following two wild-card characters in the
pattern:
% |
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 wild-card character, precede the character
with the escape character. If you don't specify the ESCAPE character,
`\' is assumed:
\% |
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 following two statements illustrate that string comparisons are case insensitive
unless one of the operands is a binary string:
mysql> select 'abc' LIKE 'ABC';
-> 1
mysql> SELECT 'abc' LIKE BINARY 'ABC';
-> 0
LIKE is allowed on numeric expressions! (This is a MySQL extension
to the ANSI SQL LIKE.)
mysql> select 10 LIKE '1%';
-> 1
Note: Because MySQL uses the C escape syntax in strings (for example, `\n'),
you must double any `\' that you use in your LIKE
strings. For example, to search for `\n', specify it as `\\n'.
To search for `\', specify it as `\\\\' (the backslashes
are stripped once by the parser and another time when the pattern match is
done, leaving a single backslash to be matched).
expr NOT LIKE pat [ESCAPE 'escape-char']
- Same as
NOT (expr LIKE pat [ESCAPE 'escape-char']).
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.
See section I Description of MySQL regular expression
syntax. Returns 1 if expr matches pat,
otherwise returns 0. RLIKE is a synonym for REGEXP,
provided for mSQL compatibility. Note: Because MySQL uses the
C escape syntax in strings (for example, `\n'), you must double
any `\' that you use in your REGEXP strings. As
of MySQL Version 3.23.4, REGEXP is case insensitive for normal
(not 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
(ISO-8859-1 Latin1 by default) when deciding the type of a character.
expr NOT REGEXP pat
-
expr NOT RLIKE pat
- Same as
NOT (expr REGEXP pat).
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
MATCH (col1,col2,...) AGAINST (expr)
-
MATCH ... AGAINST() is used for full-text search and returns
relevance - similarity measure between the text in columns (col1,col2,...)
and the query expr. Relevance is a positive floating-point number.
Zero relevance means no similarity. For MATCH ... AGAINST() to
work, a FULLTEXT index must be created first. See section
6.5.3 CREATE TABLE Syntax.
MATCH ... AGAINST() is available in MySQL Version 3.23.23 or
later. For details and usage examples see section 6.8
MySQL Full-text Search.
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 case sensitive even if the column isn't defined as BINARY
or BLOB:
mysql> select "a" = "A";
-> 1
mysql> select BINARY "a" = "A";
-> 0
BINARY was introduced in MySQL Version 3.23.0. Note that in some
context MySQL will not be able to use the index efficiently when you cast
an indexed column to BINARY.
If you want to compare a blob case-insensitively you can always convert the
blob to upper case before doing the comparison:
SELECT 'A' LIKE UPPER(blob_col) FROM table_name;
We plan to soon introduce casting between different character sets to make
string comparison even more flexible.
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!
+
- Addition:
mysql> select 3+5;
-> 8
-
- Subtraction:
mysql> select 3-5;
-> -2
*
- 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.
/
- Division:
mysql> select 3/5;
-> 0.60
Division by zero produces a NULL result:
mysql> select 102/(1-1);
-> NULL
A division will be calculated with BIGINT arithmetic only if
performed in a context where its result is converted to an integer!
All mathematical functions return NULL in case of an error.
-
- Unary
minus. Changes the sign of the argument:
mysql> select - 2;
-> -2
Note that if this operator is used with a BIGINT, the return
value is a BIGINT! This means that you should avoid using -
on integers that may have the value of -2^63!
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.
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
MOD(N,M)
-
%
- Modulo (like the
% operator in C). 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
This function is safe to use with BIGINT values.
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!
CEILING(X)
- Returns the smallest integer value not less than
X:
mysql> select CEILING(1.23);
-> 2
mysql> select CEILING(-1.23);
-> -1
Note that the return value is converted to a BIGINT!
ROUND(X)
- Returns the argument
X, rounded to the nearest integer:
mysql> select ROUND(-1.23);
-> -1
mysql> select ROUND(-1.58);
-> -2
mysql> select ROUND(1.58);
-> 2
Note that the behavior of ROUND() when the argument is half way
between two integers depends on the C library implementation. Some round to
the nearest even number, always up, always down, or always towards zero. If
you need one kind of rounding, you should use a well-defined function like
TRUNCATE() or FLOOR() instead.
ROUND(X,D)
- Returns the argument
X, rounded to a number with D
decimals. If D is 0, the result will have no decimal
point or fractional part:
mysql> select ROUND(1.298, 1);
-> 1.3
mysql> select ROUND(1.298, 0);
-> 1
EXP(X)
- Returns the value of
e (the base of natural logarithms) raised
to the power of X:
mysql> select EXP(2);
-> 7.389056
mysql> select EXP(-2);
-> 0.135335
LOG(X)
- Returns the natural logarithm of
X:
mysql> select LOG(2);
-> 0.693147
mysql> select LOG(-2);
-> NULL
If you want the log of a number X to some arbitary base B,
use the formula LOG(X)/LOG(B).
LOG10(X)
- Returns the base-10 logarithm of
X:
mysql> select LOG10(2);
-> 0.301030
mysql> select LOG10(100);
-> 2.000000
mysql> select LOG10(-100);
-> NULL
POW(X,Y)
-
POWER(X,Y)
- Returns the value of
X raised to the power of Y:
mysql> select POW(2,2);
-> 4.000000
mysql> select POW(2,-2);
-> 0.250000
SQRT(X)
- Returns the non-negative square root of
X:
mysql> select SQRT(4);
-> 2.000000
mysql> select SQRT(20);
-> 4.472136
PI()
- Returns the value of PI. The default shown number of decimals is 5, but
MySQL internally uses the full double precession for PI.
mysql> select PI();
-> 3.141593
mysql> SELECT PI()+0.000000000000000000;
-> 3.141592653589793116
COS(X)
- Returns the cosine of
X, where X is given in
radians:
mysql> select COS(PI());
-> -1.000000
SIN(X)
- Returns the sine of
X, where X is given in radians:
mysql> select SIN(PI());
-> 0.000000
TAN(X)
- Returns the tangent of
X, where X is given in
radians:
mysql> select TAN(PI()+1);
-> 1.557408
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);
-> 0.000000
mysql> select ACOS(1.0001);
-> NULL
mysql> select ACOS(0);
-> 1.570796
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);
-> 0.201358
mysql> select ASIN('foo');
-> 0.000000
ATAN(X)
- Returns the arc tangent of
X, that is, the value whose tangent
is X:
mysql> select ATAN(2);
-> 1.107149
mysql> select ATAN(-2);
-> -1.107149
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);
-> -0.785398
mysql> select ATAN2(PI(),0);
-> 1.570796
COT(X)
- Returns the cotangent of
X:
mysql> select COT(12);
-> -1.57267341
mysql> select COT(0);
-> NULL
RAND()
-
RAND(N)
- Returns a random floating-point value in the range
0 to 1.0.
If an integer argument N is specified, it is used as the seed
value:
mysql> select RAND();
-> 0.5925
mysql> select RAND(20);
-> 0.1811
mysql> select RAND(20);
-> 0.1811
mysql> select RAND();
-> 0.2079
mysql> select RAND();
-> 0.7888
You can't use a column with RAND() values in an ORDER BY
clause, because ORDER BY would evaluate the column multiple times.
In MySQL Version 3.23, you can, however, do: SELECT * FROM table_name
ORDER BY RAND() This is useful to get a random sample of a set SELECT
* FROM table1,table2 WHERE a=b AND c<d ORDER BY RAND() LIMIT 1000.
Note that a RAND() in a WHERE clause will be re-evaluated
every time the WHERE is executed.
LEAST(X,Y,...)
- 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 other cases, the arguments are compared as case-insensitive strings:
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"
In MySQL versions prior to Version 3.22.5, you can use MIN()
instead of LEAST.
GREATEST(X,Y,...)
- 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"
In MySQL versions prior to Version 3.22.5, you can use MAX()
instead of GREATEST.
DEGREES(X)
- Returns the argument
X, converted from radians to degrees:
mysql> select DEGREES(PI());
-> 180.000000
RADIANS(X)
- Returns the argument
X, converted from degrees to radians:
mysql> select RADIANS(90);
-> 1.570796
TRUNCATE(X,D)
- Returns the number
X, truncated to D decimals.
If D is 0, the result will have no decimal point
or fractional part:
mysql> select TRUNCATE(1.223,1);
-> 1.2
mysql> select TRUNCATE(1.999,1);
-> 1.9
mysql> select TRUNCATE(1.999,0);
-> 1
Note that as decimal numbers are normally not stored as exact numbers in computers,
but as double values, you may be fooled by the following result:
mysql> select TRUNCATE(10.28*100,0);
-> 1027
The above happens because 10.28 is actually stored as something like 10.2799999999999999.
See section 6.2.2 Date and Time
Types for a description of the range of values each type has and the valid
formats in which date and time values may be specified.
Here is an example that uses date functions. The query below selects all records
with a date_col value from within the last 30 days:
mysql> SELECT something FROM table
WHERE TO_DAYS(NOW()) - TO_DAYS(date_col) <= 30;
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
WEEKDAY(date)
- Returns the weekday index for
date (0 = Monday,
1 = Tuesday, ... 6 = Sunday):
mysql> select WEEKDAY('1997-10-04 22:23:00');
-> 5
mysql> select WEEKDAY('1997-11-05');
-> 2
DAYOFMONTH(date)
- Returns the day of the month for
date, in the range 1
to 31:
mysql> select DAYOFMONTH('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
MONTH(date)
- Returns the month for
date, in the range 1 to
12:
mysql> select MONTH('1998-02-03');
-> 2
DAYNAME(date)
- Returns the name of the weekday for
date:
mysql> select DAYNAME("1998-02-05");
-> 'Thursday'
MONTHNAME(date)
- Returns the name of the month for
date:
mysql> select MONTHNAME("1998-02-05");
-> 'February'
QUARTER(date)
- Returns the quarter of the year for
date, in the range 1
to 4:
mysql> select QUARTER('98-04-01');
-> 2
WEEK(date)
-
WEEK(date,first)
- With a single argument, returns the week for
date, in the
range 0 to 53 (yes, there may be the beginnings
of a week 53), for locations where Sunday is the first day of the week. The
two-argument form of WEEK() allows you to specify whether the
week starts on Sunday or Monday. The week starts on Sunday if the second argument
is 0, on Monday if the second argument is 1:
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
YEAR(date)
- Returns the year for
date, in the range 1000
to 9999:
mysql> select YEAR('98-02-03');
-> 1998
YEARWEEK(date)
-
YEARWEEK(date,first)
- Returns year and week for a date. The second arguments works exactly like
the second argument to
WEEK(). Note that the year 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
HOUR(time)
- Returns the hour for
time, in the range 0 to
23:
mysql> select HOUR('10:05:03');
-> 10
MINUTE(time)
- Returns the minute for
time, in the range 0 to
59:
mysql> select MINUTE('98-02-03 10:05:03');
-> 5
SECOND(time)
- Returns the second for
time, in the range 0 to
59:
mysql> select SECOND('10:05:03');
-> 3
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
DATE_ADD(date,INTERVAL expr type)
-
DATE_SUB(date,INTERVAL expr type)
-
ADDDATE(date,INTERVAL expr type)
-
SUBDATE(date,INTERVAL expr type)
- These functions perform date arithmetic. They are new for MySQL Version
3.22.
ADDDATE() and SUBDATE() are synonyms for DATE_ADD()
and DATE_SUB(). In MySQL Version 3.23, you can use +
and - instead of DATE_ADD() and DATE_SUB()
if the expression on the right side is a date or datetime column. (See example)
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 related function EXTRACT(type FROM date) returns the 'type'
interval from the date. The following table shows how the type
and expr arguments are related:
type value |
Expected expr format
|
SECOND |
SECONDS |
MINUTE |
MINUTES |
HOUR |
HOURS |
DAY |
DAYS |
MONTH |
MONTHS |
YEAR |
YEARS |
MINUTE_SECOND |
"MINUTES:SECONDS" |
HOUR_MINUTE |
"HOURS:MINUTES" |
DAY_HOUR |
"DAYS HOURS" |
YEAR_MONTH |
"YEARS-MONTHS" |
HOUR_SECOND |
"HOURS:MINUTES:SECONDS" |
DAY_MINUTE |
"DAYS HOURS:MINUTES" |
DAY_SECOND |
"DAYS HOURS:MINUTES:SECONDS" |
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:
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
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 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 time of day. Note that if you
add or subtract a date value against something that contains a time part,
the date value will be 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 really incorrect 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
Note from the preceding example that the word INTERVAL and the
type keyword are not case sensitive.
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
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 doesn't take into account
the days that were lost when the calendar was changed.
FROM_DAYS(N)
- Given a daynumber
N, returns a DATE value:
mysql> select FROM_DAYS(729669);
-> '1997-10-07'
FROM_DAYS() is not intended for use with values that precede
the advent of the Gregorian calendar (1582), because it doesn't take into
account the days that were lost when the calendar was changed.
DATE_FORMAT(date,format)
- Formats the
date value according to the format
string. The following specifiers may be used in the format string:
%M |
Month name (January..December) |
%W |
Weekday name (Sunday..Saturday) |
%D |
Day of the month with English suffix (1st, 2nd,
3rd, etc.) |
%Y |
Year, numeric, 4 digits |
%y |
Year, numeric, 2 digits |
%X |
Year for the week where Sunday is the first day of the week, numeric,
4 digits, used with '%V' |
%x |
Year for the week, where Monday is the first day of the week, numeric,
4 digits, used with '%v' |
%a |
Abbreviated weekday name (Sun..Sat) |
%d |
Day of the month, numeric (00..31) |
%e |
Day of the month, numeric (0..31) |
%m |
Month, numeric (01..12) |
%c |
Month, numeric (1..12) |
%b |
Abbreviated month name (Jan..Dec) |
%j |
Day of year (001..366) |
%H |
Hour (00..23) |
%k |
Hour (0..23) |
%h |
Hour (01..12) |
%I |
Hour (01..12) |
%l |
Hour (1..12) |
%i |
Minutes, numeric (00..59) |
%r |
Time, 12-hour (hh:mm:ss [AP]M) |
%T |
Time, 24-hour (hh:mm:ss) |
%S |
Seconds (00..59) |
%s |
Seconds (00..59) |
%p |
AM or PM |
%w |
Day of the week (0=Sunday..6=Saturday)
|
%U |
Week (0..53), where Sunday is the first
day of the week |
%u |
Week (0..53), where Monday is the first
day of the week |
%V |
Week (1..53), where Sunday is the first
day of the week. Used with '%X' |
%v |
Week (1..53), where Monday is the first
day of the week. Used with '%x' |
%% |
A literal `%'. |
All other characters are just copied to the result without interpretation:
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'
As of MySQL Version 3.23, the `%' character is required before
format specifier characters. In earlier versions of MySQL, `%'
was optional.
TIME_FORMAT(time,format)
- This is used like the
DATE_FORMAT() function above, but the
format string may contain only those format specifiers that handle
hours, minutes, and seconds. Other specifiers produce a NULL
value or 0.
CURDATE()
-
CURRENT_DATE
- Returns today's 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
CURTIME()
-
CURRENT_TIME
- 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
NOW()
-
SYSDATE()
-
CURRENT_TIMESTAMP
- 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
UNIX_TIMESTAMP()
-
UNIX_TIMESTAMP(date)
- If called with no argument, returns a Unix timestamp (seconds since
'1970-01-01
00:00:00' GMT). 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 will receive the value directly, with no implicit ``string-to-unix-timestamp''
conversion. If you give UNIX_TIMESTAMP() a wrong or out-of-range
date, it will return 0.
FROM_UNIXTIME(unix_timestamp)
- 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:
mysql> select FROM_UNIXTIME(875996580);
-> '1997-10-04 22:23:00'
mysql> select FROM_UNIXTIME(875996580) + 0;
-> 19971004222300
FROM_UNIXTIME(unix_timestamp,format)
- Returns a string representation of the Unix timestamp, 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(UNIX_TIMESTAMP(),
'%Y %D %M %h:%i:%s %x');
-> '1997 23rd December 03:43:30 x'
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
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
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
&
- Bitwise AND:
mysql> select 29 & 15;
-> 13
<<
- Shifts a longlong (
BIGINT) number to the left:
mysql> select 1 << 2;
-> 4
>>
- Shifts a longlong (
BIGINT) number to the right:
mysql> select 4 >> 2;
-> 1
~
- Invert all bits:
mysql> select 5 & ~1;
-> 4
BIT_COUNT(N)
- Returns the number of bits that are set in the argument
N:
mysql> select BIT_COUNT(29);
-> 4
DATABASE()
- Returns the current database name:
mysql> select DATABASE();
-> 'test'
If there is no current database, DATABASE() returns the empty
string.
USER()
-
SYSTEM_USER()
-
SESSION_USER()
- Returns the current MySQL user name:
mysql> select USER();
-> 'davida@localhost'
In MySQL Version 3.22.11 or later, this includes the client hostname as well
as the user name. You can extract just the user name part like this (which
works whether or not the value includes a hostname part):
mysql> select substring_index(USER(),"@",1);
-> 'davida'
PASSWORD(str)
- Calculates a password string from the plaintext password
str.
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');
-> '7f84554057dd964b'
PASSWORD() encryption is non-reversible.
PASSWORD() does not perform password encryption in the same way
that Unix passwords are encrypted. You should not assume that if your Unix
password and your MySQL password are the same, PASSWORD() will
result in the same encrypted value as is stored in the Unix password file.
See ENCRYPT().
ENCRYPT(str[,salt])
- Encrypt
str using the Unix crypt() system call.
The salt argument should be a string with two characters. (As
of MySQL Version 3.22.16, salt may be longer than two characters.):
mysql> select ENCRYPT("hello");
-> 'VxuFAJXVARROc'
If crypt() is not available on your system, ENCRYPT()
always returns NULL. ENCRYPT() ignores all but the
first 8 characters of str, at least on some systems. This will
be determined by the behavior of the underlying crypt() system
call.
ENCODE(str,pass_str)
- Encrypt
str using pass_str as the password. To
decrypt the result, use DECODE(). The results is a binary string
of the same length as string. If you want to save it in a column,
use a BLOB column type.
DECODE(crypt_str,pass_str)
- Descrypts the encrypted string
crypt_str using pass_str
as the password. crypt_str should be a string returned from ENCODE().
MD5(string)
- Calculates a MD5 checksum for the string. Value is returned as a 32 long
hex number that may, for example, be used as a hash key:
mysql> select MD5("testing");
-> 'ae2b1fca515949e5d54fb22b8ed95575'
This is an "RSA Data Security, Inc. MD5 Message-Digest Algorithm".
LAST_INSERT_ID([expr])
- Returns the last automatically generated value that was inserted into an
AUTO_INCREMENT column. See section 8.4.3.126
mysql_insert_id().
mysql> select LAST_INSERT_ID();
-> 195
The last ID that was generated is maintained in the server on a per-connection
basis. It will not be changed by another client. It will not even be changed
if you update another AUTO_INCREMENT column with a non-magic
value (that is, a value that is not NULL and not 0).
If you insert many rows at the same time with an insert statement, LAST_INSERT_ID()
returns the value for the first inserted row. The reason for this is so that
you it makes it possible to easily reproduce the same INSERT
statement against some other server. If expr
is given as an argument to LAST_INSERT_ID(), then the value of
the argument is returned by the function, is set as the next value to be returned
by LAST_INSERT_ID() and used as the next auto_increment value.
This can be used to simulate sequences: First create the table:
mysql> create table sequence (id int not null);
mysql> insert into sequence values (0);
Then the table can be used to generate sequence numbers like this:
mysql> update sequence set id=LAST_INSERT_ID(id+1);
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. You can retrieve
the new ID as you would read any normal AUTO_INCREMENT value
in MySQL. For example, LAST_INSERT_ID() (without an argument)
will return the new ID. The C API function mysql_insert_id()
can also be used to get the value. Note that as mysql_insert_id()
is only updated after INSERT and UPDATE statements,
you can't use this function to retrieve the value for LAST_INSERT_ID(expr)
after executing other SQL statements like SELECT or SET.
FORMAT(X,D)
- Formats the number
X to a format like '#,###,###.##',
rounded to D decimals. If D is 0, the
result will have 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'
VERSION()
- Returns a string indicating the MySQL server version:
mysql> select VERSION();
-> '3.23.13-log'
Note that if your version ends with -log this means that logging
is enabled.
CONNECTION_ID()
- Returns the connection id (
thread_id) for the connection.
Every connection has its own unique id:
mysql> select CONNECTION_ID();
-> 1
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,
or NULL if an error occurred (such as running out of memory or
the thread was killed with mysqladmin kill). A lock is released
when you execute RELEASE_LOCK(), execute a new GET_LOCK(),
or the thread terminates. This function can be used to implement application
locks or to simulate record locks. It blocks requests by other clients for
locks with the same name; clients that agree on a given lock string name can
use the string to perform cooperative advisory locking:
mysql> select GET_LOCK("lock1",10);
-> 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.
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 wasn't locked by this thread (in which case the
lock is not released), and NULL if the named lock didn't exist.
The lock will not exist if it was never obtained by a call to GET_LOCK()
or if it already has been released.
BENCHMARK(count,expr)
- The
BENCHMARK() function executes the expression expr
repeatedly count times. It may be used to time how fast MySQL
processes the expression. The result value is always 0. The intended
use is in 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 may be advisable to execute BENCHMARK() several times,
and interpret the result with regard to how heavily loaded the server machine
is.
INET_NTOA(expr)
- Returns the network address (4 or 8 byte) for the numeric expression:
mysql> select INET_NTOA(3520061480);
-> "209.207.224.40"
INET_ATON(expr)
- Returns an integer that represents the numeric value for a network 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 example the above
number is calculated as 209*255^3 + 207*255^2 + 224*255 +40.
MASTER_POS_WAIT(log_name, log_pos)
- Blocks until the slave reaches the specified position in the master log
during replication. If master information is not initialized, returns NULL.
If the slave is not running, will block and wait until it is started and goes
to or past the specified position. If the slave is already past the specified
position, returns immediately. The return value is the number of log events
it had to wait to get to the specified position, or NULL in case of error.
Useful for control of master-slave synchronization, but was originally written
to facilitate replication testing.
-
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