Table 14.12 String Functions and Operators
Name | Description |
---|---|
ASCII() |
Return numeric value of left-most character |
BIN() |
Return a string containing binary representation of a number |
BIT_LENGTH() |
Return length of argument in bits |
CHAR() |
Return the character for each integer passed |
CHAR_LENGTH() |
Return number of characters in argument |
CHARACTER_LENGTH() |
Synonym for CHAR_LENGTH() |
CONCAT() |
Return concatenated string |
CONCAT_WS() |
Return concatenate with separator |
ELT() |
Return string at index number |
EXPORT_SET() |
Return a string such that for every bit set in the value bits, you get an on string and for every unset bit, you get an off string |
FIELD() |
Index (position) of first argument in subsequent arguments |
FIND_IN_SET() |
Index (position) of first argument within second argument |
FORMAT() |
Return a number formatted to specified number of decimal places |
HEX() |
Hexadecimal representation of decimal or string value |
INSERT() |
Insert substring at specified position up to specified number of characters |
INSTR() |
Return the index of the first occurrence of substring |
LCASE() |
Synonym for LOWER() |
LEFT() |
Return the leftmost number of characters as specified |
LENGTH() |
Return the length of a string in bytes |
LIKE |
Simple pattern matching |
LOAD_FILE() |
Load the named file |
LOCATE() |
Return the position of the first occurrence of substring |
LOWER() |
Return the argument in lowercase |
LPAD() |
Return the string argument, left-padded with the specified string |
LTRIM() |
Remove leading spaces |
MAKE_SET() |
Return a set of comma-separated strings that have the corresponding bit in bits set |
MATCH() |
Perform full-text search |
MID() |
Return a substring starting from the specified position |
NOT LIKE |
Negation of simple pattern matching |
NOT REGEXP |
Negation of REGEXP |
OCT() |
Return a string containing octal representation of a number |
OCTET_LENGTH() |
Synonym for LENGTH() |
ORD() |
Return character code for leftmost character of the argument |
POSITION() |
Synonym for LOCATE() |
QUOTE() |
Escape the argument for use in an SQL statement |
REGEXP |
Whether string matches regular expression |
REGEXP_INSTR() |
Starting index of substring matching regular expression |
REGEXP_LIKE() |
Whether string matches regular expression |
REGEXP_REPLACE() |
Replace substrings matching regular expression |
REGEXP_SUBSTR() |
Return substring matching regular expression |
REPEAT() |
Repeat a string the specified number of times |
REPLACE() |
Replace occurrences of a specified string |
REVERSE() |
Reverse the characters in a string |
RIGHT() |
Return the specified rightmost number of characters |
RLIKE |
Whether string matches regular expression |
RPAD() |
Append string the specified number of times |
RTRIM() |
Remove trailing spaces |
SOUNDEX() |
Return a soundex string |
SOUNDS LIKE |
Compare sounds |
SPACE() |
Return a string of the specified number of spaces |
STRCMP() |
Compare two strings |
SUBSTR() |
Return the substring as specified |
SUBSTRING() |
Return the substring as specified |
SUBSTRING_INDEX() |
Return a substring from a string before the specified number of occurrences of the delimiter |
TRIM() |
Remove leading and trailing spaces |
UCASE() |
Synonym for UPPER() |
UNHEX() |
Return a string containing hex representation of a number |
UPPER() |
Convert to uppercase |
WEIGHT_STRING() |
Return the weight string for a string |
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 7.1.1, “Configuring the Server”.
For functions that operate on string positions, the first position is numbered 1.
For functions that take length arguments, noninteger arguments are rounded to the nearest integer.
Returns the numeric value of the leftmost character of the string
str
. Returns0
ifstr
is the empty string. ReturnsNULL
ifstr
isNULL
.ASCII()
works for 8-bit characters.mysql> SELECT ASCII('2'); -> 50 mysql> SELECT ASCII(2); -> 50 mysql> SELECT ASCII('dx'); -> 100
See also the
ORD()
function.Returns a string representation of the binary value of
N
, whereN
is a longlong (BIGINT
) number. This is equivalent toCONV(
. ReturnsN
,10,2)NULL
ifN
isNULL
.mysql> SELECT BIN(12); -> '1100'
Returns the length of the string
str
in bits. ReturnsNULL
ifstr
isNULL
.mysql> SELECT BIT_LENGTH('text'); -> 32
CHAR(
N
,... [USINGcharset_name
])CHAR()
interprets each argumentN
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'); +--------------------------------------------------+ | CHAR(77,121,83,81,'76') | +--------------------------------------------------+ | 0x4D7953514C | +--------------------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT CHAR(77,77.3,'77.3'); +--------------------------------------------+ | CHAR(77,77.3,'77.3') | +--------------------------------------------+ | 0x4D4D4D | +--------------------------------------------+ 1 row in set (0.00 sec)
By default,
CHAR()
returns a binary string. To produce a string in a given character set, use the optionalUSING
clause:mysql> SELECT CHAR(77,121,83,81,'76' USING utf8mb4); +---------------------------------------+ | CHAR(77,121,83,81,'76' USING utf8mb4) | +---------------------------------------+ | MySQL | +---------------------------------------+ 1 row in set (0.00 sec) mysql> SELECT CHAR(77,77.3,'77.3' USING utf8mb4); +------------------------------------+ | CHAR(77,77.3,'77.3' USING utf8mb4) | +------------------------------------+ | MMM | +------------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql> SHOW WARNINGS; +---------+------+-------------------------------------------+ | Level | Code | Message | +---------+------+-------------------------------------------+ | Warning | 1292 | Truncated incorrect INTEGER value: '77.3' | +---------+------+-------------------------------------------+ 1 row in set (0.00 sec)
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 fromCHAR()
becomesNULL
.If
CHAR()
is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the--binary-as-hex
. For more information about that option, see Section 6.5.1, “mysql — The MySQL Command-Line Client”.CHAR()
arguments larger than 255 are converted into multiple result bytes. For example,CHAR(256)
is equivalent toCHAR(1,0)
, andCHAR(256*256)
is equivalent toCHAR(1,0,0)
:mysql> SELECT HEX(CHAR(1,0)), HEX(CHAR(256)); +----------------+----------------+ | HEX(CHAR(1,0)) | HEX(CHAR(256)) | +----------------+----------------+ | 0100 | 0100 | +----------------+----------------+ 1 row in set (0.00 sec) mysql> SELECT HEX(CHAR(1,0,0)), HEX(CHAR(256*256)); +------------------+--------------------+ | HEX(CHAR(1,0,0)) | HEX(CHAR(256*256)) | +------------------+--------------------+ | 010000 | 010000 | +------------------+--------------------+ 1 row in set (0.00 sec)
Returns the length of the string
str
, measured in code points. A multibyte character counts as a single code point. This means that, for a string containing two 3-byte characters,LENGTH()
returns6
, whereasCHAR_LENGTH()
returns2
, as shown here:mysql> SET @dolphin:='海豚'; Query OK, 0 rows affected (0.01 sec) mysql> SELECT LENGTH(@dolphin), CHAR_LENGTH(@dolphin); +------------------+-----------------------+ | LENGTH(@dolphin) | CHAR_LENGTH(@dolphin) | +------------------+-----------------------+ | 6 | 2 | +------------------+-----------------------+ 1 row in set (0.00 sec)
CHAR_LENGTH()
returnsNULL
ifstr
isNULL
.CHARACTER_LENGTH()
is a synonym forCHAR_LENGTH()
.Returns the string that results from concatenating the arguments. May have one or more arguments. If all arguments are nonbinary strings, the result is a nonbinary string. If the arguments include any binary strings, the result is a binary string. A numeric argument is converted to its equivalent nonbinary string form.
CONCAT()
returnsNULL
if any argument isNULL
.mysql> SELECT CONCAT('My', 'S', 'QL'); -> 'MySQL' mysql> SELECT CONCAT('My', NULL, 'QL'); -> NULL mysql> SELECT CONCAT(14.3); -> '14.3'
For quoted strings, concatenation can be performed by placing the strings next to each other:
mysql> SELECT 'My' 'S' 'QL'; -> 'MySQL'
If
CONCAT()
is invoked from within the mysql client, binary string results display using hexadecimal notation, depending on the value of the--binary-as-hex
. For more information about that option, see Section 6.5.1, “mysql — The MySQL Command-Line Client”.CONCAT_WS(
separator
,str1
,str2
,...)CONCAT_WS()
stands for Concatenate With Separator and is a special form ofCONCAT()
. 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 isNULL
, the result isNULL
.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 anyNULL
values after the separator argument.ELT()
returns theN
th element of the list of strings:str1
ifN
=1
,str2
ifN
=2
, and so on. ReturnsNULL
ifN
is less than1
, greater than the number of arguments, orNULL
.ELT()
is the complement ofFIELD()
.mysql> SELECT ELT(1, 'Aa', 'Bb', 'Cc', 'Dd'); -> 'Aa' mysql> SELECT ELT(4, 'Aa', 'Bb', 'Cc', 'Dd'); -> 'Dd'
EXPORT_SET(
bits
,on
,off
[,separator
[,number_of_bits
]])Returns a string such that for every bit set in the value
bits
, you get anon
string and for every bit not set in the value, you get anoff
string. Bits inbits
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 theseparator
string (the default being the comma character,
). The number of bits examined is given bynumber_of_bits
, which has a default of 64 if not specified.number_of_bits
is silently clipped to 64 if larger than 64. It is treated as an unsigned integer, so a value of −1 is effectively the same as 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'
Returns the index (position) of
str
in thestr1
,str2
,str3
,...
list. Returns0
ifstr
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
isNULL
, the return value is0
becauseNULL
fails equality comparison with any value.FIELD()
is the complement ofELT()
.mysql> SELECT FIELD('Bb', 'Aa', 'Bb', 'Cc', 'Dd', 'Ff'); -> 2 mysql> SELECT FIELD('Gg', 'Aa', 'Bb', 'Cc', 'Dd', 'Ff'); -> 0
Returns a value in the range of 1 to
N
if the stringstr
is in the string liststrlist
consisting ofN
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 typeSET
, theFIND_IN_SET()
function is optimized to use bit arithmetic. Returns0
ifstr
is not instrlist
or ifstrlist
is the empty string. ReturnsNULL
if either argument isNULL
. 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
Formats the number
X
to a format like'#,###,###.##'
, rounded toD
decimal places, and returns the result as a string. IfD
is0
, the result has no decimal point or fractional part. IfX
orD
isNULL
, the function returnsNULL
.The optional third parameter enables a locale to be specified to be used for the result number's decimal point, thousands separator, and grouping between separators. Permissible locale values are the same as the legal values for the
lc_time_names
system variable (see Section 12.16, “MySQL Server Locale Support”). If the locale isNULL
or not specified, the default locale is'en_US'
.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' mysql> SELECT FORMAT(12332.2,2,'de_DE'); -> '12.332,20'
Takes a string encoded with the base-64 encoded rules used by
TO_BASE64()
and returns the decoded result as a binary string. The result isNULL
if the argument isNULL
or not a valid base-64 string. See the description ofTO_BASE64()
for details about the encoding and decoding rules.mysql> SELECT TO_BASE64('abc'), FROM_BASE64(TO_BASE64('abc')); -> 'JWJj', 'abc'
If
FROM_BASE64()
is invoked from within the mysql client, binary strings display using hexadecimal notation. You can disable this behavior by setting the value of the--binary-as-hex
to0
when starting the mysql client. For more information about that option, see Section 6.5.1, “mysql — The MySQL Command-Line Client”.For a string argument
str
,HEX()
returns a hexadecimal string representation ofstr
where each byte of each character instr
is converted to two hexadecimal digits. (Multibyte characters therefore become more than two digits.) The inverse of this operation is performed by theUNHEX()
function.For a numeric argument
N
,HEX()
returns a hexadecimal string representation of the value ofN
treated as a longlong (BIGINT
) number. This is equivalent toCONV(
. The inverse of this operation is performed byN
,10,16)CONV(HEX(
.N
),16,10)For a
NULL
argument, this function returnsNULL
.mysql> SELECT X'616263', HEX('abc'), UNHEX(HEX('abc')); -> 'abc', 616263, 'abc' mysql> SELECT HEX(255), CONV(HEX(255),16,10); -> 'FF', 255
Returns the string
str
, with the substring beginning at positionpos
andlen
characters long replaced by the stringnewstr
. Returns the original string ifpos
is not within the length of the string. Replaces the rest of the string from positionpos
iflen
is not within the length of the rest of the string. ReturnsNULL
if any argument isNULL
.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 multibyte safe.
Returns the position of the first occurrence of substring
substr
in stringstr
. This is the same as the two-argument form ofLOCATE()
, except that the order of the arguments is reversed.mysql> SELECT INSTR('foobarbar', 'bar'); -> 4 mysql> SELECT INSTR('xbar', 'foobar'); -> 0
This function is multibyte safe, and is case-sensitive only if at least one argument is a binary string. If either argument is
NULL
, this functions returnsNULL
.LCASE()
is a synonym forLOWER()
.LCASE()
used in a view is rewritten asLOWER()
when storing the view's definition. (Bug #12844279)Returns the leftmost
len
characters from the stringstr
, orNULL
if any argument isNULL
.mysql> SELECT LEFT('foobarbar', 5); -> 'fooba'
This function is multibyte safe.
Returns the length of the string
str
, measured in bytes. A multibyte character counts as multiple bytes. This means that for a string containing five 2-byte characters,LENGTH()
returns10
, whereasCHAR_LENGTH()
returns5
. ReturnsNULL
ifstr
isNULL
.mysql> SELECT LENGTH('text'); -> 4
NoteThe
Length()
OpenGIS spatial function is namedST_Length()
in MySQL.Reads the file and returns the file contents as a string. To use this function, the file must be located on the server host, you must specify the full path name to the file, and you must have the
FILE
privilege. The file must be readable by the server and its size less thanmax_allowed_packet
bytes. If thesecure_file_priv
system variable is set to a nonempty directory name, the file to be loaded must be located in that directory.If the file does not exist or cannot be read because one of the preceding conditions is not satisfied, the function returns
NULL
.The
character_set_filesystem
system variable controls interpretation of file names that are given as literal strings.mysql> UPDATE t SET blob_col=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 stringstr
. The second syntax returns the position of the first occurrence of substringsubstr
in stringstr
, starting at positionpos
. Returns0
ifsubstr
is not instr
. ReturnsNULL
if any argument isNULL
.mysql> SELECT LOCATE('bar', 'foobarbar'); -> 4 mysql> SELECT LOCATE('xbar', 'foobar'); -> 0 mysql> SELECT LOCATE('bar', 'foobarbar', 5); -> 7
This function is multibyte safe, and is case-sensitive only if at least one argument is a binary string.
Returns the string
str
with all characters changed to lowercase according to the current character set mapping, orNULL
ifstr
isNULL
. The default character set isutf8mb4
.mysql> SELECT LOWER('QUADRATICALLY'); -> 'quadratically'
LOWER()
(andUPPER()
) are ineffective when applied to binary strings (BINARY
,VARBINARY
,BLOB
). To perform lettercase conversion of a binary string, first convert it to a nonbinary string using a character set appropriate for the data stored in the string:mysql> SET @str = BINARY 'New York'; mysql> SELECT LOWER(@str), LOWER(CONVERT(@str USING utf8mb4)); +-------------+------------------------------------+ | LOWER(@str) | LOWER(CONVERT(@str USING utf8mb4)) | +-------------+------------------------------------+ | New York | new york | +-------------+------------------------------------+
For collations of Unicode character sets,
LOWER()
andUPPER()
work according to the Unicode Collation Algorithm (UCA) version in the collation name, if there is one, and UCA 4.0.0 if no version is specified. For example,utf8mb4_0900_ai_ci
andutf8mb3_unicode_520_ci
work according to UCA 9.0.0 and 5.2.0, respectively, whereasutf8mb3_unicode_ci
works according to UCA 4.0.0. See Section 12.10.1, “Unicode Character Sets”.This function is multibyte safe.
LCASE()
used within views is rewritten asLOWER()
.Returns the string
str
, left-padded with the stringpadstr
to a length oflen
characters. Ifstr
is longer thanlen
, the return value is shortened tolen
characters.mysql> SELECT LPAD('hi',4,'??'); -> '??hi' mysql> SELECT LPAD('hi',1,'??'); -> 'h'
Returns
NULL
if any of its arguments areNULL
.Returns the string
str
with leading space characters removed. ReturnsNULL
ifstr
isNULL
.mysql> SELECT LTRIM(' barbar'); -> 'barbar'
This function is multibyte safe.
Returns a set value (a string containing substrings separated by
,
characters) consisting of the strings that have the corresponding bit inbits
set.str1
corresponds to bit 0,str2
to bit 1, and so on.NULL
values instr1
,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
)MID(
,str
FROMpos
)MID(
,str
,pos
,len
)MID(
str
FROMpos
FORlen
)MID(
is a synonym forstr
,pos
,len
)SUBSTRING(
.str
,pos
,len
)Returns a string representation of the octal value of
N
, whereN
is a longlong (BIGINT
) number. This is equivalent toCONV(
. ReturnsN
,10,8)NULL
ifN
isNULL
.mysql> SELECT OCT(12); -> '14'
OCTET_LENGTH()
is a synonym forLENGTH()
.If the leftmost character of the string
str
is a multibyte 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 * 256^2) ...
If the leftmost character is not a multibyte character,
ORD()
returns the same value as theASCII()
function. The function returnsNULL
ifstr
isNULL
.mysql> SELECT ORD('2'); -> 50
POSITION(
is a synonym forsubstr
INstr
)LOCATE(
.substr
,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 enclosed by single quotation marks and with each instance of backslash (
\
), single quote ('
), ASCIINUL
, and Control+Z preceded by a backslash. If the argument isNULL
, the return value is the word “NULL” without enclosing single quotation marks.mysql> SELECT QUOTE('Don\'t!'); -> 'Don\'t!' mysql> SELECT QUOTE(NULL); -> NULL
For comparison, see the quoting rules for literal strings and within the C API in Section 11.1.1, “String Literals”, and mysql_real_escape_string_quote().
Returns a string consisting of the string
str
repeatedcount
times. Ifcount
is less than 1, returns an empty string. ReturnsNULL
ifstr
orcount
isNULL
.mysql> SELECT REPEAT('MySQL', 3); -> 'MySQLMySQLMySQL'
Returns the string
str
with all occurrences of the stringfrom_str
replaced by the stringto_str
.REPLACE()
performs a case-sensitive match when searching forfrom_str
.mysql> SELECT REPLACE('www.mysql.com', 'w', 'Ww'); -> 'WwWwWw.mysql.com'
This function is multibyte safe. It returns
NULL
if any of its arguments areNULL
.Returns the string
str
with the order of the characters reversed, orNULL
ifstr
isNULL
.mysql> SELECT REVERSE('abc'); -> 'cba'
This function is multibyte safe.
Returns the rightmost
len
characters from the stringstr
, orNULL
if any argument isNULL
.mysql> SELECT RIGHT('foobarbar', 4); -> 'rbar'
This function is multibyte safe.
Returns the string
str
, right-padded with the stringpadstr
to a length oflen
characters. Ifstr
is longer thanlen
, the return value is shortened tolen
characters. Ifstr
,padstr
, orlen
isNULL
, the function returnsNULL
.mysql> SELECT RPAD('hi',5,'?'); -> 'hi???' mysql> SELECT RPAD('hi',1,'?'); -> 'h'
This function is multibyte safe.
Returns the string
str
with trailing space characters removed.mysql> SELECT RTRIM('barbar '); -> 'barbar'
This function is multibyte safe, and returns
NULL
ifstr
isNULL
.Returns a soundex string from
str
, orNULL
ifstr
isNULL
. Two strings that sound almost the same should have identical soundex strings. A standard soundex string is four characters long, but theSOUNDEX()
function returns an arbitrarily long string. You can useSUBSTRING()
on the result to get a standard soundex string. All nonalphabetic characters instr
are ignored. All international alphabetic characters outside the A-Z range are treated as vowels.ImportantWhen using
SOUNDEX()
, you should be aware of the following limitations:This function, as currently implemented, is intended to work well with strings that are in the English language only. Strings in other languages may not produce reliable results.
This function is not guaranteed to provide consistent results with strings that use multibyte character sets, including
utf-8
. See Bug #22638 for more information.
mysql> SELECT SOUNDEX('Hello'); -> 'H400' mysql> SELECT SOUNDEX('Quadratically'); -> 'Q36324'
NoteThis 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 duplicates second, whereas the enhanced version discards duplicates first and vowels second.
This is the same as
SOUNDEX(
.expr1
) = SOUNDEX(expr2
)Returns a string consisting of
N
space characters, orNULL
ifN
isNULL
.mysql> SELECT SPACE(6); -> ' '
SUBSTR(
,str
,pos
)SUBSTR(
,str
FROMpos
)SUBSTR(
,str
,pos
,len
)SUBSTR(
str
FROMpos
FORlen
)SUBSTR()
is a synonym forSUBSTRING()
.SUBSTRING(
,str
,pos
)SUBSTRING(
,str
FROMpos
)SUBSTRING(
,str
,pos
,len
)SUBSTRING(
str
FROMpos
FORlen
)The forms without a
len
argument return a substring from stringstr
starting at positionpos
. The forms with alen
argument return a substringlen
characters long from stringstr
, starting at positionpos
. The forms that useFROM
are standard SQL syntax. It is also possible to use a negative value forpos
. In this case, the beginning of the substring ispos
characters from the end of the string, rather than the beginning. A negative value may be used forpos
in any of the forms of this function. A value of 0 forpos
returns an empty string.For all forms of
SUBSTRING()
, the position of the first character in the string from which the substring is to be extracted is reckoned as1
.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 multibyte safe. It returns
NULL
if any of its arguments areNULL
.If
len
is less than 1, the result is the empty string.SUBSTRING_INDEX(
str
,delim
,count
)Returns the substring from string
str
beforecount
occurrences of the delimiterdelim
. Ifcount
is positive, everything to the left of the final delimiter (counting from the left) is returned. Ifcount
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 fordelim
.mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', 2); -> 'www.mysql' mysql> SELECT SUBSTRING_INDEX('www.mysql.com', '.', -2); -> 'mysql.com'
This function is multibyte safe.
SUBSTRING_INDEX()
returnsNULL
if any of its arguments areNULL
.Converts the string argument to base-64 encoded form and returns the result as a character string with the connection character set and collation. If the argument is not a string, it is converted to a string before conversion takes place. The result is
NULL
if the argument isNULL
. Base-64 encoded strings can be decoded using theFROM_BASE64()
function.mysql> SELECT TO_BASE64('abc'), FROM_BASE64(TO_BASE64('abc')); -> 'JWJj', 'abc'
Different base-64 encoding schemes exist. These are the encoding and decoding rules used by
TO_BASE64()
andFROM_BASE64()
:The encoding for alphabet value 62 is
'+'
.The encoding for alphabet value 63 is
'/'
.Encoded output consists of groups of 4 printable characters. Each 3 bytes of the input data are encoded using 4 characters. If the last group is incomplete, it is padded with
'='
characters to a length of 4.A newline is added after each 76 characters of encoded output to divide long output into multiple lines.
Decoding recognizes and ignores newline, carriage return, tab, and space.
TRIM([{BOTH | LEADING | TRAILING} [
,remstr
] FROM]str
)TRIM([
remstr
FROM]str
)Returns the string
str
with allremstr
prefixes or suffixes removed. If none of the specifiersBOTH
,LEADING
, orTRAILING
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 multibyte safe. It returns
NULL
if any of its arguments areNULL
.UCASE()
is a synonym forUPPER()
.UCASE()
used within views is rewritten asUPPER()
.For a string argument
str
,UNHEX(
interprets each pair of characters in the argument as a hexadecimal number and converts it to the byte represented by the number. The return value is a binary string.str
)mysql> SELECT UNHEX('4D7953514C'); -> 'MySQL' mysql> SELECT X'4D7953514C'; -> 'MySQL' mysql> SELECT UNHEX(HEX('string')); -> 'string' mysql> SELECT HEX(UNHEX('1267')); -> '1267'
The characters in the argument string must be legal hexadecimal digits:
'0'
..'9'
,'A'
..'F'
,'a'
..'f'
. If the argument contains any nonhexadecimal digits, or is itselfNULL
, the result isNULL
:mysql> SELECT UNHEX('GG'); +-------------+ | UNHEX('GG') | +-------------+ | NULL | +-------------+ mysql> SELECT UNHEX(NULL); +-------------+ | UNHEX(NULL) | +-------------+ | NULL | +-------------+
A
NULL
result can also occur if the argument toUNHEX()
is aBINARY
column, because values are padded with0x00
bytes when stored but those bytes are not stripped on retrieval. For example,'41'
is stored into aCHAR(3)
column as'41 '
and retrieved as'41'
(with the trailing pad space stripped), soUNHEX()
for the column value returnsX'41'
. By contrast,'41'
is stored into aBINARY(3)
column as'41\0'
and retrieved as'41\0'
(with the trailing pad0x00
byte not stripped).'\0'
is not a legal hexadecimal digit, soUNHEX()
for the column value returnsNULL
.For a numeric argument
N
, the inverse ofHEX(
is not performed byN
)UNHEX()
. UseCONV(HEX(
instead. See the description ofN
),16,10)HEX()
.If
UNHEX()
is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the--binary-as-hex
. For more information about that option, see Section 6.5.1, “mysql — The MySQL Command-Line Client”.Returns the string
str
with all characters changed to uppercase according to the current character set mapping, orNULL
ifstr
isNULL
. The default character set isutf8mb4
.mysql> SELECT UPPER('Hej'); -> 'HEJ'
See the description of
LOWER()
for information that also applies toUPPER()
. This included information about how to perform lettercase conversion of binary strings (BINARY
,VARBINARY
,BLOB
) for which these functions are ineffective, and information about case folding for Unicode character sets.This function is multibyte safe.
UCASE()
used within views is rewritten asUPPER()
.WEIGHT_STRING(
str
[AS {CHAR|BINARY}(N
)] [flags
])This function returns the weight string for the input string. The return value is a binary string that represents the comparison and sorting value of the string, or
NULL
if the argument isNULL
. It has these properties:If
WEIGHT_STRING(
=str1
)WEIGHT_STRING(
, thenstr2
)
(str1
=str2
str1
andstr2
are considered equal)If
WEIGHT_STRING(
<str1
)WEIGHT_STRING(
, thenstr2
)
(str1
<str2
str1
sorts beforestr2
)
WEIGHT_STRING()
is a debugging function intended for internal use. Its behavior can change without notice between MySQL versions. It can be used for testing and debugging of collations, especially if you are adding a new collation. See Section 12.14, “Adding a Collation to a Character Set”.This list briefly summarizes the arguments. More details are given in the discussion following the list.
str
: The input string expression.AS
clause: Optional; cast the input string to a given type and length.flags
: Optional; unused.
The input string,
str
, is a string expression. If the input is a nonbinary (character) string such as aCHAR
,VARCHAR
, orTEXT
value, the return value contains the collation weights for the string. If the input is a binary (byte) string such as aBINARY
,VARBINARY
, orBLOB
value, the return value is the same as the input (the weight for each byte in a binary string is the byte value). If the input isNULL
,WEIGHT_STRING()
returnsNULL
.Examples:
mysql> SET @s = _utf8mb4 'AB' COLLATE utf8mb4_0900_ai_ci; mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s)); +------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | AB | 4142 | 1C471C60 | +------+---------+------------------------+
mysql> SET @s = _utf8mb4 'ab' COLLATE utf8mb4_0900_ai_ci; mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s)); +------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | ab | 6162 | 1C471C60 | +------+---------+------------------------+
mysql> SET @s = CAST('AB' AS BINARY); mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s)); +------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | AB | 4142 | 4142 | +------+---------+------------------------+
mysql> SET @s = CAST('ab' AS BINARY); mysql> SELECT @s, HEX(@s), HEX(WEIGHT_STRING(@s)); +------+---------+------------------------+ | @s | HEX(@s) | HEX(WEIGHT_STRING(@s)) | +------+---------+------------------------+ | ab | 6162 | 6162 | +------+---------+------------------------+
The preceding examples use
HEX()
to display theWEIGHT_STRING()
result. Because the result is a binary value,HEX()
can be especially useful when the result contains nonprinting values, to display it in printable form:mysql> SET @s = CONVERT(X'C39F' USING utf8mb4) COLLATE utf8mb4_czech_ci; mysql> SELECT HEX(WEIGHT_STRING(@s)); +------------------------+ | HEX(WEIGHT_STRING(@s)) | +------------------------+ | 0FEA0FEA | +------------------------+
For non-
NULL
return values, the data type of the value isVARBINARY
if its length is within the maximum length forVARBINARY
, otherwise the data type isBLOB
.The
AS
clause may be given to cast the input string to a nonbinary or binary string and to force it to a given length:AS CHAR(
casts the string to a nonbinary string and pads it on the right with spaces to a length ofN
)N
characters.N
must be at least 1. IfN
is less than the length of the input string, the string is truncated toN
characters. No warning occurs for truncation.AS BINARY(
is similar but casts the string to a binary string,N
)N
is measured in bytes (not characters), and padding uses0x00
bytes (not spaces).
mysql> SET NAMES 'latin1'; mysql> SELECT HEX(WEIGHT_STRING('ab' AS CHAR(4))); +-------------------------------------+ | HEX(WEIGHT_STRING('ab' AS CHAR(4))) | +-------------------------------------+ | 41422020 | +-------------------------------------+ mysql> SET NAMES 'utf8mb4'; mysql> SELECT HEX(WEIGHT_STRING('ab' AS CHAR(4))); +-------------------------------------+ | HEX(WEIGHT_STRING('ab' AS CHAR(4))) | +-------------------------------------+ | 1C471C60 | +-------------------------------------+
mysql> SELECT HEX(WEIGHT_STRING('ab' AS BINARY(4))); +---------------------------------------+ | HEX(WEIGHT_STRING('ab' AS BINARY(4))) | +---------------------------------------+ | 61620000 | +---------------------------------------+
The
flags
clause currently is unused.If
WEIGHT_STRING()
is invoked from within the mysql client, binary strings display using hexadecimal notation, depending on the value of the--binary-as-hex
. For more information about that option, see Section 6.5.1, “mysql — The MySQL Command-Line Client”.