String Functions and Operators
6.4. 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 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 6-6. These functions are also implemented using the regular syntax for function invocation. (See Table 6-7.)
Table 6-6. 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 6-8 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 | Insert 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 beginning/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 6-7. Some of them are used internally to implement the SQL-standard string functions listed in Table 6-6.
Table 6-7. 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, trim text) | text | Remove (trim) the longest string consisting only of characters in trim 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 |
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 | Length of 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, text text) | text | Remove the longest string containing only characters from trim from the start of the string. | ltrim('zzzytrim','xyz') | trim |
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 query 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 literal in an SQL query 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, trim text) | text | Remove the longest string containing only characters from trim from the end of the string. | rtrim('trimxxxx','x') | trim |
split_part(string text,
delimiter text,
column integer) | text | Split string on delimiter returning the resulting (one based) column number. | split_part('abc~@~def~@~ghi','~@~',2) | def |
strpos(string, substring) | text | Locate specified substring (same as position(substring in string), but note the reversed argument order) | strpos('high','ig') | 2 |
substr(string, from [, count]) | text | Extract specified 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(9223372036854775807::bigint) | 7fffffffffffffff |
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 6-8. 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. | ||