Chapter 92. String Functions

Table of Contents

String Comparison Functions
Case-Sensitivity

String-valued functions return NULL if the length of the result would be greater than the max_allowed_packet server parameter. See 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.
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,...)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'
    
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.
    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
    
COMPRESS() was added in MySQL version 4.1.1. It requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL. The compressed string contents are stored the following way:
  • Empty strings are stored as empty strings.

  • Non-empty strings are stored as a 4-byte length of the uncompressed string (low byte first), followed by the string compressed with gzip. If the string ends with space, we add an extra . to avoid problems with end space 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 more than 2 arguments. A numeric argument is converted to its 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 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'
    
Before MySQL 4.0.14, CONCAT_WS() skips empty strings as well as NULL values.
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 where for every bit set in bits, 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
    
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 comma ,:
    mysql> SELECT FIND_IN_SET('b','a,b,c,d');
            -> 2
    
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 of N_OR_S where each character in N_OR_S is converted to 2 hexadecimal digits. This is the inverse of the 0xff strings.
    mysql> SELECT HEX(255);
            -> 'FF'
    mysql> SELECT HEX("abc");
            -> 616263
    mysql> SELECT 0x616263;
            -> "abc"
    
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.
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. In MySQL 3.23 this function is case sensitive, while in 4.0 it's only case sensitive if either 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 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 tbl_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.
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. In MySQL 3.23 this function is case sensitive, while in 4.0 it's only case sensitive if either 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 ISO-8859-1 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'
    
LTRIM(str) Returns the string str with leading space characters removed:
    mysql> SELECT LTRIM('  barbar');
            -> 'barbar'
    
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');
            -> ''
    
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 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 ASCII code values of its constituent characters using this formula: ((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 that the ASCII() function does:
    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. The QUOTE() function was added in MySQL version 4.0.3.
    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:
    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???'
    
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 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'
    
expr1 SOUNDS LIKE expr2 Same as SOUNDEX(expr1)=SOUNDEX(expr2) (available only in version 4.1 or later).
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 SQL-92 syntax.
    mysql> SELECT SUBSTRING('Quadratically',5);
            -> 'ratically'
    mysql> SELECT SUBSTRING('foobarbar' FROM 4);
            -> 'barbar'
    mysql> SELECT SUBSTRING('Quadratically',5,6);
            -> 'ratica'
    
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.
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.
UCASE(str)UCASE() is a synonym for UPPER().
UNCOMPRESS(string_to_uncompress) Uncompresses a string compressed by the COMPRESS() function.
    mysql> SELECT UNCOMPRESS(COMPRESS("any string"));
            -> 'any string'
    
UNCOMPRESS() was added in MySQL version 4.1.1. It requires MySQL to have been compiled with a compression library such as zlib. Otherwise, the return value is always NULL.
UNCOMPRESSED_LENGTH(compressed_string) Returns the length of a compressed string before compressing.
    mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT("a",30)));
            -> 30
    
UNCOMPRESSED_LENGTH() was added in MySQL version 4.1.1.
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 UPPER('Hej');
            -> 'HEJ'
    
This function is multi-byte safe.

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, 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 wildcard characters in the pattern:
CharDescription
%Matches any number of characters, even zero characters
_Matches exactly one character
StringDescription
\%Matches one % character
\_Matches one _ character
MATCH (col1,col2,...) AGAINST (expr [IN BOOLEAN MODE | WITH QUERY EXPANSION] )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. MATCH ... AGAINST() is available in MySQL version 3.23.23 or later. IN BOOLEAN MODE extension was added in version 4.0.1, WITH QUERY EXPANSION was added in 4.1.1. For details and usage examples, see Fulltext Search.   
expr NOT LIKE pat [ESCAPE 'escape-char'] Same as NOT (expr LIKE pat [ESCAPE 'escape-char']).   
expr NOT REGEXP pat , expr NOT RLIKE pat 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. See Regexp. 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 not case sensitive 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.
  
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
    
As of MySQL 4.0, 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. Before MySQL 4.0, STRCMP() is case sensitive.