## 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 9.5, “SQL String Functions and Operators”. These functions are also implemented using the regular syntax for function invocation. (See Table 9.6, “Other String Functions”.)

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`)` | `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 9.7, “Built-in Conversions” 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 uppercase | `upper('tom')` | `TOM`

Additional string manipulation functions are available and are listed in Table 9.6, “Other String Functions”. Some of them are used internally to implement the SQL-standard string functions listed in Table 9.5, “SQL String Functions and Operators”.

Table 9.6. 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 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` `text`)` | `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` (a space by default) from the start of `string`. | `ltrim('zzzytrim', 'xyz')` | `trim`
``md5`(`string` `text`)` | `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. | `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 quotes and backslashes are properly doubled. | `quote_literal( 'O\'Reilly')` | `'O''Reilly'`
``repeat`(`string` `text`, `number` `integer`)` | `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`
``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` (a space by default) from the end of `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 another 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`
[a] The `to_ascii` function supports conversion from `LATIN1`, `LATIN2`, and `WIN1250` only.

Table 9.7. 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`
[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.