PostgreSQL 7.4 Documentation
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# 9.4. String Functions and Operators

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 9-6. These functions are also implemented using the regular syntax for function invocation. (See Table 9-7.)

Table 9-6. SQL String Functions and Operators

Function | Return Type | Description | Example | Result
--- | --- | --- | --- | ---
string || string | `text` | String concatenation | 'Post' || 'greSQL' | PostgreSQL
`bit_length`(string) | `integer` | Number of bits in string | bit_length('jose') | 32
`char_length`(string) or `character_length`(string) | `integer` | Number of characters in string | char_length('jose') | 4
`convert`(string using conversion_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 9-8 for available conversion names. | convert('PostgreSQL' using iso_8859_1_to_utf_8) | 'PostgreSQL' in Unicode (UTF-8) encoding
`lower`(string) | `text` | Convert string to lower case | lower('TOM') | tom
`octet_length`(string) | `integer` | Number of bytes in string | octet_length('jose') | 4
`overlay`(string placing string from `integer` [for `integer`]) | `text` | Replace substring | overlay('Txxxxas' placing 'hom' from 2 for 4) | Thomas
`position`(substring in string) | `integer` | Location of specified substring | position('om' in 'Thomas') | 3
`substring`(string [from `integer`] [for `integer`]) | `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 pattern for 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 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`(`text`) | integer | ASCII code of the first character of the argument | ascii('x') | 120
`btrim`(string `text`, characters `text`) | `text` | Remove the longest string consisting only of characters in characters from the start and end of string. | btrim('xyxtrimyyx', 'xy') | trim
`chr`(`integer`) | `text` | Character with the given ASCII code | chr(65) | A
`convert`(string `text`, [src_encoding `name`,] 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_unicode', 'UNICODE', 'LATIN1') | text_in_unicode represented 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 ASCII-only representation. Supported types are: base64, hex, escape. | encode( '123\\000\\001', 'base64') | MTIzAAE=
`initcap`(`text`) | `text` | Convert first letter of each word (whitespace-separated) to upper case | initcap('hi thomas') | Hi Thomas
`length`(string) | `integer` | Number of characters in string | length('jose') | 4
`lpad`(string `text`, length `integer` [, 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 from the start of the string. | ltrim('zzzytrim', 'xyz') | trim
`md5`(string `text`) | `text` | Calculates the MD5 hash of given 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. | quote_ident('Foo') | "Foo"
`quote_literal`(string text) | `text` | Return the given string suitably quoted to be used as a string literal in an SQL statement string. Embedded quotes and backslashes are properly doubled. | quote_literal( 'O\'Reilly') | 'O''Reilly'
`repeat`(`text`, `integer`) | `text` | Repeat text a 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
`rpad`(string `text`, length `integer` [, 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 from the end of the string. | rtrim('trimxxxx', 'x') | trim
`split_part`(string `text`, delimiter `text`, field `integer`) | `text` | Split string on delimiter and return the given field (counting from one) | split_part( 'abc~@~def~@~ghi', '~@~', 2) | def
`strpos`(string, substring) | `text` | 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`(`text` [, encoding]) | `text` | Convert text to ASCII from other encoding [a] | to_ascii('Karel') | Karel
`to_hex`(number `integer` 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. | translate('12345', '14', 'ax') | a23x5
Notes: a. The `to_ascii` function supports conversion from LATIN1, LATIN2, and WIN1250 only.

Table 9-8. Built-in Conversions

Conversion Name [a] | Source Encoding | Destination Encoding
--- | --- | ---
ascii_to_mic | SQL_ASCII | MULE_INTERNAL
ascii_to_utf_8 | SQL_ASCII | UNICODE
big5_to_euc_tw | BIG5 | EUC_TW
big5_to_mic | BIG5 | MULE_INTERNAL
big5_to_utf_8 | BIG5 | UNICODE
euc_cn_to_mic | EUC_CN | MULE_INTERNAL
euc_cn_to_utf_8 | EUC_CN | UNICODE
euc_jp_to_mic | EUC_JP | MULE_INTERNAL
euc_jp_to_sjis | EUC_JP | SJIS
euc_jp_to_utf_8 | EUC_JP | UNICODE
euc_kr_to_mic | EUC_KR | MULE_INTERNAL
euc_kr_to_utf_8 | EUC_KR | UNICODE
euc_tw_to_big5 | EUC_TW | BIG5
euc_tw_to_mic | EUC_TW | MULE_INTERNAL
euc_tw_to_utf_8 | EUC_TW | UNICODE
gb18030_to_utf_8 | GB18030 | UNICODE
gbk_to_utf_8 | GBK | UNICODE
iso_8859_10_to_utf_8 | LATIN6 | UNICODE
iso_8859_13_to_utf_8 | LATIN7 | UNICODE
iso_8859_14_to_utf_8 | LATIN8 | UNICODE
iso_8859_15_to_utf_8 | LATIN9 | UNICODE
iso_8859_16_to_utf_8 | LATIN10 | UNICODE
iso_8859_1_to_mic | LATIN1 | MULE_INTERNAL
iso_8859_1_to_utf_8 | LATIN1 | UNICODE
iso_8859_2_to_mic | LATIN2 | MULE_INTERNAL
iso_8859_2_to_utf_8 | LATIN2 | UNICODE
iso_8859_2_to_windows_1250 | LATIN2 | WIN1250
iso_8859_3_to_mic | LATIN3 | MULE_INTERNAL
iso_8859_3_to_utf_8 | LATIN3 | UNICODE
iso_8859_4_to_mic | LATIN4 | MULE_INTERNAL
iso_8859_4_to_utf_8 | LATIN4 | UNICODE
iso_8859_5_to_koi8_r | ISO_8859_5 | KOI8
iso_8859_5_to_mic | ISO_8859_5 | MULE_INTERNAL
iso_8859_5_to_utf_8 | ISO_8859_5 | UNICODE
iso_8859_5_to_windows_1251 | ISO_8859_5 | WIN
iso_8859_5_to_windows_866 | ISO_8859_5 | ALT
iso_8859_6_to_utf_8 | ISO_8859_6 | UNICODE
iso_8859_7_to_utf_8 | ISO_8859_7 | UNICODE
iso_8859_8_to_utf_8 | ISO_8859_8 | UNICODE
iso_8859_9_to_utf_8 | LATIN5 | UNICODE
johab_to_utf_8 | JOHAB | UNICODE
koi8_r_to_iso_8859_5 | KOI8 | ISO_8859_5
koi8_r_to_mic | KOI8 | MULE_INTERNAL
koi8_r_to_utf_8 | KOI8 | UNICODE
koi8_r_to_windows_1251 | KOI8 | WIN
koi8_r_to_windows_866 | KOI8 | ALT
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 | KOI8
mic_to_sjis | MULE_INTERNAL | SJIS
mic_to_windows_1250 | MULE_INTERNAL | WIN1250
mic_to_windows_1251 | MULE_INTERNAL | WIN
mic_to_windows_866 | MULE_INTERNAL | ALT
sjis_to_euc_jp | SJIS | EUC_JP
sjis_to_mic | SJIS | MULE_INTERNAL
sjis_to_utf_8 | SJIS | UNICODE
tcvn_to_utf_8 | TCVN | UNICODE
uhc_to_utf_8 | UHC | UNICODE
utf_8_to_ascii | UNICODE | SQL_ASCII
utf_8_to_big5 | UNICODE | BIG5
utf_8_to_euc_cn | UNICODE | EUC_CN
utf_8_to_euc_jp | UNICODE | EUC_JP
utf_8_to_euc_kr | UNICODE | EUC_KR
utf_8_to_euc_tw | UNICODE | EUC_TW
utf_8_to_gb18030 | UNICODE | GB18030
utf_8_to_gbk | UNICODE | GBK
utf_8_to_iso_8859_1 | UNICODE | LATIN1
utf_8_to_iso_8859_10 | UNICODE | LATIN6
utf_8_to_iso_8859_13 | UNICODE | LATIN7
utf_8_to_iso_8859_14 | UNICODE | LATIN8
utf_8_to_iso_8859_15 | UNICODE | LATIN9
utf_8_to_iso_8859_16 | UNICODE | LATIN10
utf_8_to_iso_8859_2 | UNICODE | LATIN2
utf_8_to_iso_8859_3 | UNICODE | LATIN3
utf_8_to_iso_8859_4 | UNICODE | LATIN4
utf_8_to_iso_8859_5 | UNICODE | ISO_8859_5
utf_8_to_iso_8859_6 | UNICODE | ISO_8859_6
utf_8_to_iso_8859_7 | UNICODE | ISO_8859_7
utf_8_to_iso_8859_8 | UNICODE | ISO_8859_8
utf_8_to_iso_8859_9 | UNICODE | LATIN5
utf_8_to_johab | UNICODE | JOHAB
utf_8_to_koi8_r | UNICODE | KOI8
utf_8_to_sjis | UNICODE | SJIS
utf_8_to_tcvn | UNICODE | TCVN
utf_8_to_uhc | UNICODE | UHC
utf_8_to_windows_1250 | UNICODE | WIN1250
utf_8_to_windows_1251 | UNICODE | WIN
utf_8_to_windows_1256 | UNICODE | WIN1256
utf_8_to_windows_866 | UNICODE | ALT
utf_8_to_windows_874 | UNICODE | WIN874
windows_1250_to_iso_8859_2 | WIN1250 | LATIN2
windows_1250_to_mic | WIN1250 | MULE_INTERNAL
windows_1250_to_utf_8 | WIN1250 | UNICODE
windows_1251_to_iso_8859_5 | WIN | ISO_8859_5
windows_1251_to_koi8_r | WIN | KOI8
windows_1251_to_mic | WIN | MULE_INTERNAL
windows_1251_to_utf_8 | WIN | UNICODE
windows_1251_to_windows_866 | WIN | ALT
windows_1256_to_utf_8 | WIN1256 | UNICODE
windows_866_to_iso_8859_5 | ALT | ISO_8859_5
windows_866_to_koi8_r | ALT | KOI8
windows_866_to_mic | ALT | MULE_INTERNAL
windows_866_to_utf_8 | ALT | UNICODE
windows_866_to_windows_1251 | ALT | WIN
windows_874_to_utf_8 | WIN874 | UNICODE
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 equally processed destination encoding name. Therefore the names might deviate from the customary encoding names.

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