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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 9-5. These functions are also implemented using the regular syntax for function invocation. (See Table 9-6.)

Table 9-5. SQL String Functions and Operators

FunctionReturn TypeDescriptionExampleResult
string || string text String concatenation 'Post' || 'greSQL'PostgreSQL
bit_length(string)intNumber of bits in stringbit_length('jose')32
char_length(string) or character_length(string)int 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 for available conversion names. convert('PostgreSQL' using iso_8859_1_to_utf8)'PostgreSQL' in UTF8 (Unicode, 8-bit) encoding
lower(string)textConvert string to lower caselower('TOM')tom
octet_length(string)intNumber of bytes in stringoctet_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)intLocation of specified substringposition('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 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)textConvert string to uppercaseupper('tom')TOM

Additional string manipulation functions are available and are listed in Table 9-6. Some of them are used internally to implement the SQL-standard string functions listed in Table 9-5.

Table 9-6. Other String Functions

FunctionReturn TypeDescriptionExampleResult
ascii(text)intASCII code of the first character of the argumentascii('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', 'xy')trim
chr(int)textCharacter with the given ASCII codechr(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_utf8', 'UTF8', 'LATIN1')text_in_utf8 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)int Number of characters in string length('jose')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('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 int)textRepeat string the specified number of timesrepeat('Pg', 4)PgPgPgPg
replace(string text, from text, to text)textReplace all occurrences in string of substring from with substring to replace( 'abcdefabcdef', 'cd', 'XX')abXXefabXXef
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('trimxxxx', 'x')trim
split_part(string text, delimiter text, field int)textSplit 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(text [, encoding])text Convert text to ASCII from another encoding [a] to_ascii('Karel')Karel
to_hex(number int or bigint)textConvert 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, LATIN9, and WIN1250 encodings only.

Table 9-7. Built-in Conversions

Conversion Name [a] Source EncodingDestination Encoding
ascii_to_micSQL_ASCIIMULE_INTERNAL
ascii_to_utf8SQL_ASCIIUTF8
big5_to_euc_twBIG5EUC_TW
big5_to_micBIG5MULE_INTERNAL
big5_to_utf8BIG5UTF8
euc_cn_to_micEUC_CNMULE_INTERNAL
euc_cn_to_utf8EUC_CNUTF8
euc_jp_to_micEUC_JPMULE_INTERNAL
euc_jp_to_sjisEUC_JPSJIS
euc_jp_to_utf8EUC_JPUTF8
euc_kr_to_micEUC_KRMULE_INTERNAL
euc_kr_to_utf8EUC_KRUTF8
euc_tw_to_big5EUC_TWBIG5
euc_tw_to_micEUC_TWMULE_INTERNAL
euc_tw_to_utf8EUC_TWUTF8
gb18030_to_utf8GB18030UTF8
gbk_to_utf8GBKUTF8
iso_8859_10_to_utf8LATIN6UTF8
iso_8859_13_to_utf8LATIN7UTF8
iso_8859_14_to_utf8LATIN8UTF8
iso_8859_15_to_utf8LATIN9UTF8
iso_8859_16_to_utf8LATIN10UTF8
iso_8859_1_to_micLATIN1MULE_INTERNAL
iso_8859_1_to_utf8LATIN1UTF8
iso_8859_2_to_micLATIN2MULE_INTERNAL
iso_8859_2_to_utf8LATIN2UTF8
iso_8859_2_to_windows_1250LATIN2WIN1250
iso_8859_3_to_micLATIN3MULE_INTERNAL
iso_8859_3_to_utf8LATIN3UTF8
iso_8859_4_to_micLATIN4MULE_INTERNAL
iso_8859_4_to_utf8LATIN4UTF8
iso_8859_5_to_koi8_rISO_8859_5KOI8
iso_8859_5_to_micISO_8859_5MULE_INTERNAL
iso_8859_5_to_utf8ISO_8859_5UTF8
iso_8859_5_to_windows_1251ISO_8859_5WIN1251
iso_8859_5_to_windows_866ISO_8859_5WIN866
iso_8859_6_to_utf8ISO_8859_6UTF8
iso_8859_7_to_utf8ISO_8859_7UTF8
iso_8859_8_to_utf8ISO_8859_8UTF8
iso_8859_9_to_utf8LATIN5UTF8
johab_to_utf8JOHABUTF8
koi8_r_to_iso_8859_5KOI8ISO_8859_5
koi8_r_to_micKOI8MULE_INTERNAL
koi8_r_to_utf8KOI8UTF8
koi8_r_to_windows_1251KOI8WIN1251
koi8_r_to_windows_866KOI8WIN866
mic_to_asciiMULE_INTERNALSQL_ASCII
mic_to_big5MULE_INTERNALBIG5
mic_to_euc_cnMULE_INTERNALEUC_CN
mic_to_euc_jpMULE_INTERNALEUC_JP
mic_to_euc_krMULE_INTERNALEUC_KR
mic_to_euc_twMULE_INTERNALEUC_TW
mic_to_iso_8859_1MULE_INTERNALLATIN1
mic_to_iso_8859_2MULE_INTERNALLATIN2
mic_to_iso_8859_3MULE_INTERNALLATIN3
mic_to_iso_8859_4MULE_INTERNALLATIN4
mic_to_iso_8859_5MULE_INTERNALISO_8859_5
mic_to_koi8_rMULE_INTERNALKOI8
mic_to_sjisMULE_INTERNALSJIS
mic_to_windows_1250MULE_INTERNALWIN1250
mic_to_windows_1251MULE_INTERNALWIN1251
mic_to_windows_866MULE_INTERNALWIN866
sjis_to_euc_jpSJISEUC_JP
sjis_to_micSJISMULE_INTERNAL
sjis_to_utf8SJISUTF8
tcvn_to_utf8WIN1258UTF8
uhc_to_utf8UHCUTF8
utf8_to_asciiUTF8SQL_ASCII
utf8_to_big5UTF8BIG5
utf8_to_euc_cnUTF8EUC_CN
utf8_to_euc_jpUTF8EUC_JP
utf8_to_euc_krUTF8EUC_KR
utf8_to_euc_twUTF8EUC_TW
utf8_to_gb18030UTF8GB18030
utf8_to_gbkUTF8GBK
utf8_to_iso_8859_1UTF8LATIN1
utf8_to_iso_8859_10UTF8LATIN6
utf8_to_iso_8859_13UTF8LATIN7
utf8_to_iso_8859_14UTF8LATIN8
utf8_to_iso_8859_15UTF8LATIN9
utf8_to_iso_8859_16UTF8LATIN10
utf8_to_iso_8859_2UTF8LATIN2
utf8_to_iso_8859_3UTF8LATIN3
utf8_to_iso_8859_4UTF8LATIN4
utf8_to_iso_8859_5UTF8ISO_8859_5
utf8_to_iso_8859_6UTF8ISO_8859_6
utf8_to_iso_8859_7UTF8ISO_8859_7
utf8_to_iso_8859_8UTF8ISO_8859_8
utf8_to_iso_8859_9UTF8LATIN5
utf8_to_johabUTF8JOHAB
utf8_to_koi8_rUTF8KOI8
utf8_to_sjisUTF8SJIS
utf8_to_tcvnUTF8WIN1258
utf8_to_uhcUTF8UHC
utf8_to_windows_1250UTF8WIN1250
utf8_to_windows_1251UTF8WIN1251
utf8_to_windows_1252UTF8WIN1252
utf8_to_windows_1256UTF8WIN1256
utf8_to_windows_866UTF8WIN866
utf8_to_windows_874UTF8WIN874
windows_1250_to_iso_8859_2WIN1250LATIN2
windows_1250_to_micWIN1250MULE_INTERNAL
windows_1250_to_utf8WIN1250UTF8
windows_1251_to_iso_8859_5WIN1251ISO_8859_5
windows_1251_to_koi8_rWIN1251KOI8
windows_1251_to_micWIN1251MULE_INTERNAL
windows_1251_to_utf8WIN1251UTF8
windows_1251_to_windows_866WIN1251WIN866
windows_1252_to_utf8WIN1252UTF8
windows_1256_to_utf8WIN1256UTF8
windows_866_to_iso_8859_5WIN866ISO_8859_5
windows_866_to_koi8_rWIN866KOI8
windows_866_to_micWIN866MULE_INTERNAL
windows_866_to_utf8WIN866UTF8
windows_866_to_windows_1251WIN866WIN
windows_874_to_utf8WIN874UTF8
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.