PostgreSQL string functions and operators

function	return type	describe	example	result
string || string	text	string concatenation	'Post'丨丨'greSQL'	PostgreSQL
bit_length(string)	int	the number of binary bits in the string	bit_length('jose')	32
char_length(string)	int	the number of characters in the string	char_length('jose')	4
convert(string using conversion_name)	text	Change the encoding using the specified conversion name.	convert('PostgreSQL' using iso_8859_1_to_utf8)	'PostgreSQL'
lower(string)	text	convert string to lowercase	lower('TOM')	tom
octet_length(string)	int	the number of bytes in the 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	the position of the specified substring	position('om' in 'Thomas')	3
substring(string [from int] [for int])	text	extract substring	substring('Thomas' from 2 for 3)	him
substring(string from pattern)	text	extract substring matching POSIX regular expression	substring('Thomas' from '…$')	but
substring(string from pattern for escape)	text	Extract substring matching SQL regular expression	substring('Thomas' from '%#"o_a#"_' for '#')	own
trim([leading丨trailing 丨 both] [characters] from string)	text	Remove the longest string containing only characters (default is a blank) from the beginning/end/both sides of string	trim(both 'x' from 'xTomxx')	Tom
upper(string)	text	Convert a string to uppercase.	upper('tom')	TOM
ascii(text)	int	The ASCII code of the first character of the parameter	ascii('x')	120
btrim(string text [, characters text])	text	Remove the longest string of characters only contained in characters (blank by default) from the beginning and end of string	btrim('xyxtrimyyx','xy')	trim
chr(int)	text	Gives the ASCII code for the character	chr(65)	A
convert(string text, [src_encoding name,] dest_encoding name)	text	Convert string to dest_encoding	convert( 'text_in_utf8', 'UTF8', 'LATIN1')	text_in_utf8 expressed in ISO 8859-1 encoding
initcap(text)	text	Capitalize the first consonant of each word and keep the rest lowercase. A word is a sequence 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 the string with the length length by filling the character fill (default is blank). Truncates string (on the right) if it is already longer than length.	lpad('hi', 5, 'xy')	xyxhi
ltrim(string text [, characters text])	text	Remove the longest string containing only characters (a blank by default) from the beginning of string.	ltrim('zzzytrim','xyz')	trim
md5(string text)	text	Computes the MD5 hash of the given string, returning the result in hexadecimal.	md5('abc')
repeat(string text, number int)	text	Repeat string number times.	repeat('Pg', 4)	PgPgPgPg
replace(string text, from text, to text)	text	Replace all occurrences of the substring from in the string string with the substring to.	replace('abcdefabcdef', 'cd', 'XX')	abXXefabXXef
rpad(string text, length int [, fill text])	text	Fill the string with the length length by filling the character fill (default is blank). If string is already longer than length it is truncated.	rpad('hi', 5, 'xy')	hixyx
rtrim(string text [, character text])	text	Remove the longest character containing only character (blank by default) from the end of string	rtrim('trimxxxx','x')	trim
split_part(string text, delimiter text, field int)	text	根据delimiter分隔string返回生成的第field个子字串(1 Base)。	split_part('abc~@~def~@~ghi', '~@~', 2)	def
strpos(string, substring)	text	声明的子字串的位置。	strpos('high','ig')	2
substr(string, from [, count])	text	抽取子字串。	substr('alphabet', 3, 2)	ph
to_ascii(text [, encoding])	text	把text从其它编码转换为ASCII。	to_ascii('Karel')	Karel
to_hex(number int/bigint)	text	把number转换成其对应地十六进制表现形式。	to_hex(9223372036854775807)	7fffffffffffffff
translate(string text, from text, to text)	text	把在string中包含的任何匹配from中的字符的字符转化为对应的在to中的字符。	translate('12345', '14', 'ax')	a23x5