String Functions and Operators

PostgreSQL 9.2.22 Documentation
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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 9-6 . PostgreSQL also provides versions of these functions that use the regular function invocation syntax (see Table 9-7 ).

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 9-6 . For other cases, insert an explicit coercion to text if you need to duplicate the previous behavior.

Table 9-6. 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`
`upper( string )`	`text`	Convert string to upper case	`upper('tom')`	`TOM`

Additional string manipulation functions are available and are listed in Table 9-7 . Some of them are used internally to implement the SQL -standard string functions listed in Table 9-6 .

Table 9-7. 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 all arguments. NULL arguments are ignored.	`concat('abcde', 2, NULL, 22)`	`abcde222`
`concat_ws( sep text , str "any" [, str "any" [, ...] ])`	`text`	Concatenate all but first arguments with separators. The first parameter is used as a separator. 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 9-8 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(E'123\\000\\001', 'base64')`	`MTIzAAE=`
`format ( formatstr text [, str "any" [, ...] ])`	`text`	Format a string. This function is similar to the C function `sprintf` ; but only the following conversion specifications are recognized: `%s` interpolates the corresponding argument as a string; `%I` escapes its argument as an SQL identifier; `%L` escapes its argument as an SQL literal; `%%` outputs a literal `%` . A conversion can reference an explicit parameter position by preceding the conversion specifier with `n $` , where `n` is the argument position. See also Example 39-1 .	`format('Hello %s, %1$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`
`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 39-1 .	`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 39-1 .	`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 39-1 .	`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_matches( string text , pattern text [, flags text ])`	`setof text[]`	Return all captured substrings resulting from matching a POSIX regular expression against the `string` . See Section 9.7.3 for more information.	`regexp_matches('foobarbequebaz', '(bar)(beque)')`	`{bar,beque}`
`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', E'\\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', E'\\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`
`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`

See also the aggregate function string_agg in Section 9.20 .

Table 9-8. Built-in Conversions

Conversion Name [a]	Source Encoding	Destination Encoding
`ascii_to_mic`	`SQL_ASCII`	`MULE_INTERNAL`
`ascii_to_utf8`	`SQL_ASCII`	`UTF8`
`big5_to_euc_tw`	`BIG5`	`EUC_TW`
`big5_to_mic`	`BIG5`	`MULE_INTERNAL`
`big5_to_utf8`	`BIG5`	`UTF8`
`euc_cn_to_mic`	`EUC_CN`	`MULE_INTERNAL`
`euc_cn_to_utf8`	`EUC_CN`	`UTF8`
`euc_jp_to_mic`	`EUC_JP`	`MULE_INTERNAL`
`euc_jp_to_sjis`	`EUC_JP`	`SJIS`
`euc_jp_to_utf8`	`EUC_JP`	`UTF8`
`euc_kr_to_mic`	`EUC_KR`	`MULE_INTERNAL`
`euc_kr_to_utf8`	`EUC_KR`	`UTF8`
`euc_tw_to_big5`	`EUC_TW`	`BIG5`
`euc_tw_to_mic`	`EUC_TW`	`MULE_INTERNAL`
`euc_tw_to_utf8`	`EUC_TW`	`UTF8`
`gb18030_to_utf8`	`GB18030`	`UTF8`
`gbk_to_utf8`	`GBK`	`UTF8`
`iso_8859_10_to_utf8`	`LATIN6`	`UTF8`
`iso_8859_13_to_utf8`	`LATIN7`	`UTF8`
`iso_8859_14_to_utf8`	`LATIN8`	`UTF8`
`iso_8859_15_to_utf8`	`LATIN9`	`UTF8`
`iso_8859_16_to_utf8`	`LATIN10`	`UTF8`
`iso_8859_1_to_mic`	`LATIN1`	`MULE_INTERNAL`
`iso_8859_1_to_utf8`	`LATIN1`	`UTF8`
`iso_8859_2_to_mic`	`LATIN2`	`MULE_INTERNAL`
`iso_8859_2_to_utf8`	`LATIN2`	`UTF8`
`iso_8859_2_to_windows_1250`	`LATIN2`	`WIN1250`
`iso_8859_3_to_mic`	`LATIN3`	`MULE_INTERNAL`
`iso_8859_3_to_utf8`	`LATIN3`	`UTF8`
`iso_8859_4_to_mic`	`LATIN4`	`MULE_INTERNAL`
`iso_8859_4_to_utf8`	`LATIN4`	`UTF8`
`iso_8859_5_to_koi8_r`	`ISO_8859_5`	`KOI8R`
`iso_8859_5_to_mic`	`ISO_8859_5`	`MULE_INTERNAL`
`iso_8859_5_to_utf8`	`ISO_8859_5`	`UTF8`
`iso_8859_5_to_windows_1251`	`ISO_8859_5`	`WIN1251`
`iso_8859_5_to_windows_866`	`ISO_8859_5`	`WIN866`
`iso_8859_6_to_utf8`	`ISO_8859_6`	`UTF8`
`iso_8859_7_to_utf8`	`ISO_8859_7`	`UTF8`
`iso_8859_8_to_utf8`	`ISO_8859_8`	`UTF8`
`iso_8859_9_to_utf8`	`LATIN5`	`UTF8`
`johab_to_utf8`	`JOHAB`	`UTF8`
`koi8_r_to_iso_8859_5`	`KOI8R`	`ISO_8859_5`
`koi8_r_to_mic`	`KOI8R`	`MULE_INTERNAL`
`koi8_r_to_utf8`	`KOI8R`	`UTF8`
`koi8_r_to_windows_1251`	`KOI8R`	`WIN1251`
`koi8_r_to_windows_866`	`KOI8R`	`WIN866`
`koi8_u_to_utf8`	`KOI8U`	`UTF8`
`mic_to_ascii`	`MULE_INTERNAL`	`SQL_ASCII`
`mic_to_big5`	`MULE_INTERNAL`	`BIG5`
`mic_to_euc_cn`	`MULE_INTERNAL`	`EUC_CN`
`mic_to_euc_jp`	`MULE_INTERNAL`	`EUC_JP`
`mic_to_euc_kr`	`MULE_INTERNAL`	`EUC_KR`
`mic_to_euc_tw`	`MULE_INTERNAL`	`EUC_TW`
`mic_to_iso_8859_1`	`MULE_INTERNAL`	`LATIN1`
`mic_to_iso_8859_2`	`MULE_INTERNAL`	`LATIN2`
`mic_to_iso_8859_3`	`MULE_INTERNAL`	`LATIN3`
`mic_to_iso_8859_4`	`MULE_INTERNAL`	`LATIN4`
`mic_to_iso_8859_5`	`MULE_INTERNAL`	`ISO_8859_5`
`mic_to_koi8_r`	`MULE_INTERNAL`	`KOI8R`
`mic_to_sjis`	`MULE_INTERNAL`	`SJIS`
`mic_to_windows_1250`	`MULE_INTERNAL`	`WIN1250`
`mic_to_windows_1251`	`MULE_INTERNAL`	`WIN1251`
`mic_to_windows_866`	`MULE_INTERNAL`	`WIN866`
`sjis_to_euc_jp`	`SJIS`	`EUC_JP`
`sjis_to_mic`	`SJIS`	`MULE_INTERNAL`
`sjis_to_utf8`	`SJIS`	`UTF8`
`tcvn_to_utf8`	`WIN1258`	`UTF8`
`uhc_to_utf8`	`UHC`	`UTF8`
`utf8_to_ascii`	`UTF8`	`SQL_ASCII`
`utf8_to_big5`	`UTF8`	`BIG5`
`utf8_to_euc_cn`	`UTF8`	`EUC_CN`
`utf8_to_euc_jp`	`UTF8`	`EUC_JP`
`utf8_to_euc_kr`	`UTF8`	`EUC_KR`
`utf8_to_euc_tw`	`UTF8`	`EUC_TW`
`utf8_to_gb18030`	`UTF8`	`GB18030`
`utf8_to_gbk`	`UTF8`	`GBK`
`utf8_to_iso_8859_1`	`UTF8`	`LATIN1`
`utf8_to_iso_8859_10`	`UTF8`	`LATIN6`
`utf8_to_iso_8859_13`	`UTF8`	`LATIN7`
`utf8_to_iso_8859_14`	`UTF8`	`LATIN8`
`utf8_to_iso_8859_15`	`UTF8`	`LATIN9`
`utf8_to_iso_8859_16`	`UTF8`	`LATIN10`
`utf8_to_iso_8859_2`	`UTF8`	`LATIN2`
`utf8_to_iso_8859_3`	`UTF8`	`LATIN3`
`utf8_to_iso_8859_4`	`UTF8`	`LATIN4`
`utf8_to_iso_8859_5`	`UTF8`	`ISO_8859_5`
`utf8_to_iso_8859_6`	`UTF8`	`ISO_8859_6`
`utf8_to_iso_8859_7`	`UTF8`	`ISO_8859_7`
`utf8_to_iso_8859_8`	`UTF8`	`ISO_8859_8`
`utf8_to_iso_8859_9`	`UTF8`	`LATIN5`
`utf8_to_johab`	`UTF8`	`JOHAB`
`utf8_to_koi8_r`	`UTF8`	`KOI8R`
`utf8_to_koi8_u`	`UTF8`	`KOI8U`
`utf8_to_sjis`	`UTF8`	`SJIS`
`utf8_to_tcvn`	`UTF8`	`WIN1258`
`utf8_to_uhc`	`UTF8`	`UHC`
`utf8_to_windows_1250`	`UTF8`	`WIN1250`
`utf8_to_windows_1251`	`UTF8`	`WIN1251`
`utf8_to_windows_1252`	`UTF8`	`WIN1252`
`utf8_to_windows_1253`	`UTF8`	`WIN1253`
`utf8_to_windows_1254`	`UTF8`	`WIN1254`
`utf8_to_windows_1255`	`UTF8`	`WIN1255`
`utf8_to_windows_1256`	`UTF8`	`WIN1256`
`utf8_to_windows_1257`	`UTF8`	`WIN1257`
`utf8_to_windows_866`	`UTF8`	`WIN866`
`utf8_to_windows_874`	`UTF8`	`WIN874`
`windows_1250_to_iso_8859_2`	`WIN1250`	`LATIN2`
`windows_1250_to_mic`	`WIN1250`	`MULE_INTERNAL`
`windows_1250_to_utf8`	`WIN1250`	`UTF8`
`windows_1251_to_iso_8859_5`	`WIN1251`	`ISO_8859_5`
`windows_1251_to_koi8_r`	`WIN1251`	`KOI8R`
`windows_1251_to_mic`	`WIN1251`	`MULE_INTERNAL`
`windows_1251_to_utf8`	`WIN1251`	`UTF8`
`windows_1251_to_windows_866`	`WIN1251`	`WIN866`
`windows_1252_to_utf8`	`WIN1252`	`UTF8`
`windows_1256_to_utf8`	`WIN1256`	`UTF8`
`windows_866_to_iso_8859_5`	`WIN866`	`ISO_8859_5`
`windows_866_to_koi8_r`	`WIN866`	`KOI8R`
`windows_866_to_mic`	`WIN866`	`MULE_INTERNAL`
`windows_866_to_utf8`	`WIN866`	`UTF8`
`windows_866_to_windows_1251`	`WIN866`	`WIN`
`windows_874_to_utf8`	`WIN874`	`UTF8`
`euc_jis_2004_to_utf8`	`EUC_JIS_2004`	`UTF8`
`utf8_to_euc_jis_2004`	`UTF8`	`EUC_JIS_2004`
`shift_jis_2004_to_utf8`	`SHIFT_JIS_2004`	`UTF8`
`utf8_to_shift_jis_2004`	`UTF8`	`SHIFT_JIS_2004`
`euc_jis_2004_to_shift_jis_2004`	`EUC_JIS_2004`	`SHIFT_JIS_2004`
`shift_jis_2004_to_euc_jis_2004`	`SHIFT_JIS_2004`	`EUC_JIS_2004`
Notes: a. The conversion names follow a standard naming scheme: The official name of the source encoding with all non-alphanumeric characters replaced by underscores, followed by `_to_` , followed by the similarly processed destination encoding name. Therefore, the names might deviate from the customary encoding names.

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