PostgreSQL String Functions and Operators – Quick Reference

This section describes functions and operators for examining and manipulating string values. Strings in this context include values of all the types character, character varying, and text. Unless otherwise noted, all of the functions listed below work on all of these types, but be wary of potential effects of the automatic padding when using the character type. Generally, the functions described here also work on data of non-string types by converting that data to a string representation first. Some functions also exist natively for the bit-string types.

SQL defines some string functions with a special syntax where certain key words rather than commas are used to separate the arguments. Details are in Table 9-5*. These functions are also implemented using the regular syntax for function invocation. (See Table 9-6*)

Table 9-5. SQL String Functions and Operators

Function Return Type Description Example Result
string || string text String concatenation ‘Post’ || ‘greSQL’ PostgreSQL
bit_length(string) int Number of bits in string bit_length(‘jose’) 32
char_length(string) orcharacter_length(string) int Number of characters in string char_length(‘jose’) 4
convert(string usingconversion_name) text Change encoding using specified conversion name. Conversions can be defined by CREATE CONVERSION. Also there are some pre-defined conversion names. See Table 9-7 for available conversion names. convert(‘PostgreSQL’ using iso_8859_1_to_utf8) ‘PostgreSQL’ in UTF8 (Unicode, 8-bit) encoding
lower(string) text Convert string to lower case lower(‘TOM’) tom
octet_length(string) int Number of bytes in string octet_length(‘jose’) 4
overlay(string placing stringfrom int [for int]) text Replace substring overlay(‘Txxxxas’ placing ‘hom’ from 2 for 4) Thomas
position(substring in string) int Location of specified substring position(‘om’ in ‘Thomas’) 3
substring(string [from int] [forint]) text Extract substring substring(‘Thomas’ from 2 for 3) hom
substring(string from pattern) text Extract substring matching POSIX regular expression. substring(‘Thomas’ from ‘…$’) mas
substring(string from patternfor escape) text Extract substring matching SQL regular expression substring(‘Thomas’ from ‘%#”o_a#”_’ for ‘#’) oma
trim([leading | trailing | both] [characters] from string) text Remove the longest string containing only the characters (a space by default) from the start/end/both ends of the string trim(both ‘x’ from ‘xTomxx’) Tom
upper(string) text Convert string to uppercase upper(‘tom’) TOM

Additional string manipulation functions are available and are listed in Table 9-6*. Some of them are used internally to implement the SQL-standard string functions listed in Table 9-5*. Table 9-6. Other String Functions

Function Return Type Description Example Result
ascii(string) int ASCII code of the first byte of the argument ascii(‘x’) 120
btrim(string text [, characterstext]) text Remove the longest string consisting only of characters in characters (a space by default) from the start and end ofstring btrim(‘xyxtrimyyx’, ‘xy’) trim
chr(int) text Character with the given ASCII code chr(65) A
convert(string text, [src_encodingname,] dest_encoding name) text Convert string to dest_encoding. The original encoding is specified by src_encoding. If src_encoding is omitted, database encoding is assumed. convert( ‘text_in_utf8’, ‘UTF8’, ‘LATIN1’) text_in_utf8represented in ISO 8859-1 encoding
decode(string text, type text) bytea Decode binary data from string previously encoded with encode. Parameter type is same as in encode. decode(‘MTIzAAE=’, ‘base64’) 123\000\001
encode(data bytea, type text) text Encode binary data to different representation. Supported types are: base64, hex, escape. Escape merely outputs null bytes as \000 and doubles backslashes. encode( E’123\\000\\001′, ‘base64’) MTIzAAE=
initcap(string) text Convert the first letter of each word to uppercase and the rest to lowercase. Words are sequences of alphanumeric characters separated by non-alphanumeric characters. initcap(‘hi THOMAS’) Hi Thomas
length(string) int Number of characters in string length(‘jose’) 4
lpad(string text, length int [,fill text]) text Fill up the string to length length by prepending the characters fill (a space by default). If the string is already longer than length then it is truncated (on the right). lpad(‘hi’, 5, ‘xy’) xyxhi
ltrim(string text [, characterstext]) text Remove the longest string containing only characters from characters (a space by default) from the start of string ltrim(‘zzzytrim’, ‘xyz’) trim
md5(string) text Calculates the MD5 hash of string, returning the result in hexadecimal md5(‘abc’) 900150983cd24fb0 d6963f7d28e17f72
pg_client_encoding() name Current client encoding name pg_client_encoding() SQL_ASCII
quote_ident(string) text Return the given string suitably quoted to be used as an identifier in an SQL statement string. Quotes are added only if necessary (i.e., if the string contains non-identifier characters or would be case-folded). Embedded quotes are properly doubled. quote_ident(‘Foo bar’) “Foo bar”
quote_literal(string) text Return the given string suitably quoted to be used as a string literal in an SQL statement string. Embedded single-quotes and backslashes are properly doubled. quote_literal( ‘O\’Reilly’) ‘O”Reilly’
regexp_replace(string text, patterntext, replacement text [,flagstext]) text Replace substring matching POSIX regular expression. regexp_replace(‘Thomas’, ‘.[mN]a.’, ‘M’) ThM
repeat(string text, number int) text Repeat string the specified number of times repeat(‘Pg’, 4) PgPgPgPg
replace(string text, from text, totext) text Replace all occurrences in string of substring from with substring to replace( ‘abcdefabcdef’, ‘cd’, ‘XX’) abXXefabXXef
rpad(string text, length int [,fill text]) text Fill up the string to length length by appending the characters fill (a space by default). If the string is already longer than length then it is truncated. rpad(‘hi’, 5, ‘xy’) hixyx
rtrim(string text [, characterstext]) text Remove the longest string containing only characters from characters (a space by default) from the end of string rtrim(‘trimxxxx’, ‘x’) trim
split_part(string text, delimitertext, field int) text Split string on delimiter and return the given field (counting from one) split_part(‘abc~@~def~@~ghi’, ‘~@~’, 2) def
strpos(string, substring) int Location of specified substring (same as position(substring in string), but note the reversed argument order) strpos(‘high’, ‘ig’) 2
substr(string, from [, count]) text Extract substring (same as substring(string from from for count)) substr(‘alphabet’, 3, 2) ph
to_ascii(string text [, encodingtext]) text Convert string to ASCII from another encoding (only supports conversion from LATIN1, LATIN2, LATIN9, and WIN1250encodings) to_ascii(‘Karel’) Karel
to_hex(number int or bigint) text Convert number to its equivalent hexadecimal representation to_hex(2147483647) 7fffffff
translate(string text, from text,to text) text Any character in string that matches a character in the from set is replaced by the corresponding character in the toset translate(‘12345′, ’14’, ‘ax’) a23x5

*Source: http://www.postgresql.org