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9.4. String Functions and Operators
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9.4. String Functions and Operators

9.4.1. format

This section describes functions and operators for examining and manipulating string values. Strings in this context include values of 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 automatic space-padding when using the character type. Some functions also exist natively for the bit-string types.

SQL defines some string functions that use key words, rather than commas, to separate arguments. Details are in Table 9.8. PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9.9).

Note

Before PostgreSQL 8.3, these functions would silently accept values of several non-string data types as well, due to the presence of implicit coercions from those data types to text. Those coercions have been removed because they frequently caused surprising behaviors. However, the string concatenation operator (||) still accepts non-string input, so long as at least one input is of a string type, as shown in Table 9.8. For other cases, insert an explicit coercion to text if you need to duplicate the previous behavior.

Table 9.8. SQL String Functions and Operators

Function Return Type Description Example Result
string || string text String concatenation 'Post' || 'greSQL' PostgreSQL
string || non-string or non-string || string text String concatenation with one non-string input 'Value: ' || 42 Value: 42
bit_length(string) int Number of bits in string bit_length('jose') 32
char_length(string) or character_length(string) int Number of characters in string char_length('jose') 4
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 string from 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] [for int]) text Extract substring substring('Thomas' from 2 for 3) hom
substring(string from pattern) text Extract substring matching POSIX regular expression. See Section 9.7 for more information on pattern matching. substring('Thomas' from '...$') mas
substring(string from pattern for escape) text Extract substring matching SQL regular expression. See Section 9.7 for more information on pattern matching. substring('Thomas' from '%#"o_a#"_' for '#') oma
trim([leading | trailing | both] [characters] from string) text Remove the longest string containing only characters from characters (a space by default) from the start, end, or both ends (both is the default) of string trim(both 'xyz' from 'yxTomxx') Tom
trim([leading | trailing | both] [from] string [, characters] ) text Non-standard syntax for trim() trim(both from 'yxTomxx', 'xyz') Tom
upper(string) text Convert string to upper case upper('tom') TOM

Additional string manipulation functions are available and are listed in Table 9.9. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.8.

Table 9.9. Other String Functions

Function Return Type Description Example Result
ascii(string) int ASCII code of the first character of the argument. For UTF8 returns the Unicode code point of the character. For other multibyte encodings, the argument must be an ASCII character. ascii('x') 120
btrim(string text [, characters text]) text Remove the longest string consisting only of characters in characters (a space by default) from the start and end of string btrim('xyxtrimyyx', 'xyz') trim
chr(int) text Character with the given code. For UTF8 the argument is treated as a Unicode code point. For other multibyte encodings the argument must designate an ASCII character. The NULL (0) character is not allowed because text data types cannot store such bytes. chr(65) A
concat(str "any" [, str "any" [, ...] ]) text Concatenate the text representations of all the arguments. NULL arguments are ignored. concat('abcde', 2, NULL, 22) abcde222
concat_ws(sep text, str "any" [, str "any" [, ...] ]) text Concatenate all but the first argument with separators. The first argument is used as the separator string. NULL arguments are ignored. concat_ws(',', 'abcde', 2, NULL, 22) abcde,2,22
convert(string bytea, src_encoding name, dest_encoding name) bytea Convert string to dest_encoding. The original encoding is specified by src_encoding. The string must be valid in this encoding. Conversions can be defined by CREATE CONVERSION. Also there are some predefined conversions. See Table 9.10 for available conversions. convert('text_in_utf8', 'UTF8', 'LATIN1') text_in_utf8 represented in Latin-1 encoding (ISO 8859-1)
convert_from(string bytea, src_encoding name) text Convert string to the database encoding. The original encoding is specified by src_encoding. The string must be valid in this encoding. convert_from('text_in_utf8', 'UTF8') text_in_utf8 represented in the current database encoding
convert_to(string text, dest_encoding name) bytea Convert string to dest_encoding. convert_to('some text', 'UTF8') some text represented in the UTF8 encoding
decode(string text, format text) bytea Decode binary data from textual representation in string. Options for format are same as in encode. decode('MTIzAAE=', 'base64') \x3132330001
encode(data bytea, format text) text Encode binary data into a textual representation. Supported formats are: base64, hex, escape. escape converts zero bytes and high-bit-set bytes to octal sequences (\nnn) and doubles backslashes. encode('123\000\001', 'base64') MTIzAAE=
format(formatstr text [, formatarg "any" [, ...] ]) text Format arguments according to a format string. This function is similar to the C function sprintf. See Section 9.4.1. format('Hello %s, %1$s', 'World') Hello World, World
initcap(string) text Convert the first letter of each word to upper case and the rest to lower case. Words are sequences of alphanumeric characters separated by non-alphanumeric characters. initcap('hi THOMAS') Hi Thomas
left(str text, n int) text Return first n characters in the string. When n is negative, return all but last |n| characters. left('abcde', 2) ab
length(string) int Number of characters in string length('jose') 4
length(string bytea, encoding name ) int Number of characters in string in the given encoding. The string must be valid in this encoding. length('jose', 'UTF8') 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 [, characters text]) text Remove the longest string containing only characters from characters (a space by default) from the start of string ltrim('zzzytest', 'xyz') test
md5(string) text Calculates the MD5 hash of string, returning the result in hexadecimal md5('abc') 900150983cd24fb0 d6963f7d28e17f72
parse_ident(qualified_identifier text [, strictmode boolean DEFAULT true ] ) text[] Split qualified_identifier into an array of identifiers, removing any quoting of individual identifiers. By default, extra characters after the last identifier are considered an error; but if the second parameter is false, then such extra characters are ignored. (This behavior is useful for parsing names for objects like functions.) Note that this function does not truncate over-length identifiers. If you want truncation you can cast the result to name[]. parse_ident('"SomeSchema".someTable') {SomeSchema,sometable}
pg_client_encoding() name Current client encoding name pg_client_encoding() SQL_ASCII
quote_ident(string text) 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. See also Example 43.1. quote_ident('Foo bar') "Foo bar"
quote_literal(string text) 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. Note that quote_literal returns null on null input; if the argument might be null, quote_nullable is often more suitable. See also Example 43.1. quote_literal(E'O\'Reilly') 'O''Reilly'
quote_literal(value anyelement) text Coerce the given value to text and then quote it as a literal. Embedded single-quotes and backslashes are properly doubled. quote_literal(42.5) '42.5'
quote_nullable(string text) text Return the given string suitably quoted to be used as a string literal in an SQL statement string; or, if the argument is null, return NULL. Embedded single-quotes and backslashes are properly doubled. See also Example 43.1. quote_nullable(NULL) NULL
quote_nullable(value anyelement) text Coerce the given value to text and then quote it as a literal; or, if the argument is null, return NULL. Embedded single-quotes and backslashes are properly doubled. quote_nullable(42.5) '42.5'
regexp_match(string text, pattern text [, flags text]) text[] Return captured substring(s) resulting from the first match of a POSIX regular expression to the string. See Section 9.7.3 for more information. regexp_match('foobarbequebaz', '(bar)(beque)') {bar,beque}
regexp_matches(string text, pattern text [, flags text]) setof text[] Return captured substring(s) resulting from matching a POSIX regular expression to the string. See Section 9.7.3 for more information. regexp_matches('foobarbequebaz', 'ba.', 'g') {bar}

{baz}

(2 rows)
regexp_replace(string text, pattern text, replacement text [, flags text]) text Replace substring(s) matching a POSIX regular expression. See Section 9.7.3 for more information. regexp_replace('Thomas', '.[mN]a.', 'M') ThM
regexp_split_to_array(string text, pattern text [, flags text ]) text[] Split string using a POSIX regular expression as the delimiter. See Section 9.7.3 for more information. regexp_split_to_array('hello world', '\s+') {hello,world}
regexp_split_to_table(string text, pattern text [, flags text]) setof text Split string using a POSIX regular expression as the delimiter. See Section 9.7.3 for more information. regexp_split_to_table('hello world', '\s+') hello

world

(2 rows)
repeat(string text, number int) text Repeat string the specified number of times repeat('Pg', 4) PgPgPgPg
replace(string text, from text, to text) text Replace all occurrences in string of substring from with substring to replace('abcdefabcdef', 'cd', 'XX') abXXefabXXef
reverse(str) text Return reversed string. reverse('abcde') edcba
right(str text, n int) text Return last n characters in the string. When n is negative, return all but first |n| characters. right('abcde', 2) de
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 [, characters text]) text Remove the longest string containing only characters from characters (a space by default) from the end of string rtrim('testxxzx', 'xyz') test
split_part(string text, delimiter text, 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
starts_with(string, prefix) bool Returns true if string starts with prefix. starts_with('alphabet', 'alph') t
to_ascii(string text [, encoding text]) text Convert string to ASCII from another encoding (only supports conversion from LATIN1, LATIN2, LATIN9, and WIN1250 encodings) 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 to set. If from is longer than to, occurrences of the extra characters in from are removed. translate('12345', '143', 'ax') a2x5

The concat, concat_ws and format functions are variadic, so it is possible to pass the values to be concatenated or formatted as an array marked with the VARIADIC keyword (see Section 38.5.5). The array's elements are treated as if they were separate ordinary arguments to the function. If the variadic array argument is NULL, concat and concat_ws return NULL, but format treats a NULL as a zero-element array.

See also the aggregate function string_agg in Section 9.20.

Table 9.10. Built-in Conversions

Conversion Name