函数：string || string　
说明：String concatenation字符串连接操作
例子：'Post' || 'gresql'　＝　Postgresql

函数：string || non-string or non-string ||string
说明：String concatenation with one non-string input字符串与非字符串类型进行连接操作
例子：'Value: ' || 42 = Value: 42

函数：bit_length(string)
说明：Number of bits in string 计算字符串的位数
例子：bit_length('jose') = 32

函数：char_length(string) orcharacter_length(string)
说明：Number of characters in string 计算字符串中字符个数
例子：char_length('jose') = 4

函数：lower(string)
说明：Convert string to lower case 转换字符串为小写
例子：bit_length('jose') = 32

函数：octet_length(string)
说明：Number of bytes in string 计算字符串的字节数
例子：octet_length('jose') = 4

函数：overlay(string placing string from int [forint])
说明：Replace substring 替换字符串中任意长度的子字串为新字符串
例子：overlay('Txxxxas' placing 'hom' from 2 for 4) = 4

函数：position(substring instring)
说明：Location of specified substring 子串在一字符串中的位置
例子：position('om' in 'Thomas') = 3

函数：substring(string [from int] [forint])
说明：Extract substring 截取任意长度的子字符串
例子：substring('Thomas' from 2 for 3) = hom

函数：substring(string frompattern)
说明：Extract substring matching POSIX regular expression. See Section9.7 for more information on pattern matching.利用正则表达式对一字符串进行任意长度的字串的截取
例子：substring('Thomas' from '...$') = mas

函数：substring(string from pattern forescape)
说明：Extract substring matching sql regular expression. See Section9.7 for more information on pattern matching.利于正则表达式对某类字符进行删除，以得到子字符串
例子：trim(both 'x' from 'xTomxx') = Tom

函数：trim([leading | trailing | both][characters] from string)
说明：Remove the longest string containing only the characters (aspace by default) from the start/end/both ends of the string去除尽可能长开始，结束或者两边的某类字符，默认为去除空白字符，当然可以自己指定，可同时指定多个要删除的字符串
例子：trim(both 'x' from 'xTomxx') = Tom

函数：upper(string)
说明：Convert string to uppercase 将字符串转换为大写
例子：upper('tom') = TOM

函数：ascii(string)
说明：ASCII code of the first character of the argument. For UTF8returns the Unicode code point of the character. For othermultibyte encodings. the argument must be a strictly ASCIIcharacter. 得到某一个字符的Assii值
例子：ascii('x') = 120

函数：btrim(string text [,characterstext])
说明：Remove the longest string consisting only of characters incharacters (a space by default) from the start and end of string去除字符串两边的所有指定的字符，可同时指定多个字符
例子：btrim('xyxtrimyyx','xy') = trim

函数：chr(int)
说明：Character with the given code. For UTF8 the argument is treatedas a Unicode code point. For other multibyte encodings the argumentmust designate a strictly ASCII character. The NULL (0) characteris not allowed because text data types cannot store such bytes.得到某ACSII值对应的字符
例子：chr(65) = A

函数：convert(string bytea,src_encoding name,dest_encoding name)
说明：Convert string todest_encoding. The original encoding is specified by src_encoding.The string must be valid in this encoding. Conversions can bedefined by CREATE CONVERSION. Also there are some predefinedconversions. See Table 9-7 for available conversions.转换字符串编码，指定源编码与目标编码
例子：convert('text_in_utf8','UTF8','LATIN1') = text_in_utf8represented in ISO 8859-1 encoding

函数：convert_from(string bytea,src_encodingname)
说明：Convert string to the databaseencoding. The original encoding is specified by src_encoding. Thestring must be valid in this encoding.转换字符串编码，自己要指定源编码,目标编码默认为数据库指定编码，
例子：convert_from('text_in_utf8','UTF8') = text_in_utf8 representedin the current database encoding

函数：convert_to(string text,dest_encodingname)
说明：Convert string todest_encoding.转换字符串编码，源编码默认为数据库指定编码，自己要指定目标编码,
例子：convert_to('some text','UTF8') = some text represented in theUTF8 encoding

函数：decode(string text,typetext)
说明：Decode binary data from stringprevIoUsly encoded with encode. Parameter type is same as inencode. 对字符串按指定的类型进行解码
例子：decode('MTIzAAE=','base64') = 123\000\001

函数：encode(data bytea,typetext)
说明：Encode binary data todifferent representation. Supported types are: base64,hex,escape.Escape merely outputs null bytes as \000 and doubles backslashes.与decode相反，对字符串按指定类型进行编码
例子：encode(E'123\\000\\001','base64') = MTIzAAE=

函数：initcap(string)
说明：Convert the first letter ofeach word to uppercase and the rest to lowercase. Words aresequences of alphanumeric characters separated by non-alphanumericcharacters. 将字符串所有的单词进行格式化，首字母大写，其它为小写
例子：initcap('hi THOMAS') = Hi Thomas

函数：length(string)
说明：Number of characters in string讲算字符串长度
例子：length('jose') = 4

函数：length(stringbytea,encoding name)
说明：Number ofcharacters in string in the given encoding. The string must bevalid in this encoding. 计算字符串长度，指定字符串使用的编码
例子：length('jose','UTF8') = 4

函数：lpad(string text,length int [,filltext])
说明：Fill up the string to lengthlength by prepending the characters fill (a space by default). Ifthe string is already longer than length then it is truncated (onthe right).对字符串左边进行某类字符自动填充，即不足某一长度，则在左边自动补上指定的字符串，直至达到指定长度，可同时指定多个自动填充的字符
例子：lpad('hi',5,'xy') = xyxhi

函数：ltrim(string text [,characterstext])
说明：Remove the longest stringcontaining only characters from characters (a space by default)from the start of string 删除字符串左边某一些的字符，可以时指定多个要删除的字符
例子：trim

函数：md5(string)
说明：Calculates the MD5 hash ofstring,returning the result in hexadecimal 将字符串进行md5编码
例子：md5('abc') = 900150983cd24fb0 d6963f7d28e17f72

函数：pg_client_encoding()
说明：Current client encoding name得到pg客户端编码
例子：pg_client_encoding() = sql_ASCII

函数：quote_ident(string text)
说明：Return the given stringsuitably quoted to be used as an identifier in an sql statementstring. Quotes are added only if necessary (i.e.,if the stringcontains non-identifier characters or would be case-folded).Embedded quotes are properly doubled. 对某一字符串加上两引号
例子：quote_ident('Foo bar') = "Foo bar"

函数：quote_literal(string text)
说明：Return the given stringsuitably quoted to be used as a string literal in an sql statementstring. Embedded single-quotes and backslashes are properlydoubled. 对字符串里两边加上单引号，如果字符串里面出现sql编码的单个单引号，则会被表达成两个单引号
例子：quote_literal('O\'Reilly') = 'O''Reilly'

函数：quote_literal(value anyelement)
说明：Coerce the given value to textand then quote it as a literal. Embedded single-quotes andbackslashes are properly doubled.将一数值转换为字符串，并为其两边加上单引号，如果数值中间出现了单引号，也会被表示成两个单引号
例子：quote_literal(42.5) = '42.5'

函数：regexp_matches(string text,pattern text [,flags text])
说明：Returnall captured substrings resulting from matching a POSIX regularexpression against the string. See Section 9.7.3 for moreinformation. 对字符串按正则表达式进行匹配，如果存在则会在结果数组中表示出来
例子：regexp_matches('foobarbequebaz','(bar)(beque)') ={bar,beque}

函数：regexp_replace(string text,pattern text,replacement text [,flags text])
说明：Replace substring(s) matchinga POSIX regular expression. See Section 9.7.3 for more information.利用正则表达式对字符串进行替换
例子：regexp_replace('Thomas','.[mN]a.','M') = ThM

函数：regexp_split_to_array(string text,patterntext [,flags text ])
说明：Split string using a POSIXregular expression as the delimiter. See Section 9.7.3 for moreinformation. 利用正则表达式将字符串分割成数组
例子：regexp_split_to_array('hello world',E'\\s+') ={hello,world}

函数：regexp_split_to_table(string text,flags text])
说明：Split string using a POSIXregular expression as the delimiter. See Section 9.7.3 for moreinformation. 利用正则表达式将字符串分割成表格
例子：regexp_split_to_table('hello world',E'\\s+')=
hello
world
(2 rows)

函数：repeat(string text,number int)
说明：Repeat string the specifiednumber of times 重复字符串一指定次数
例子：repeat('Pg',4) = PgPgPgPg

函数：replace(string text,from text,totext)
说明：Replace alloccurrences in string of substring from with substring to将字符的某一子串替换成另一子串
例子：('abcdefabcdef','cd','XX') = abXXefabXXef

函数：rpad(string text,filltext])
说明：Fill up the string to lengthlength by appending the characters fill (a space by default). Ifthe string is already longer than length then it is truncated.对字符串进行填充，填充内容为指定的字符串
例子：rpad('hi','xy') = hixyx

函数：rtrim(string text [,characterstext])
说明：Remove thelongest string containing only characters from characters (a spaceby default) from the end of string
去除字符串右边指定的字符
例子：rtrim('trimxxxx','x') = trim

函数：split_part(string text,delimiter text,field int)
说明：Splitstring on delimiter and return the given field (counting from one)对字符串按指定子串进行分割，并返回指定的数值位置的值
例子：split_part('abc~@~def~@~ghi','~@~',2) = def

函数：strpos(string,substring)
说明：Location of specifiedsubstring (same as position(substring in string),but note thereversed argument order) 指定字符串在目标字符串的位置
例子：strpos('high','ig') = 2

函数：substr(string,from [,count])
说明：Extract substring (same assubstring(string from from for count)) 截取子串
例子：substr('alphabet',3,2) = ph

函数：to_ascii(string text [,encodingtext])
说明：Convert stringto ASCII from another encoding (only supports conversion fromLATIN1,LATIN2,LATIN9,and WIN1250 encodings)将字符串转换成ascii编码字符串
例子：to_ascii('Karel') = Karel

函数：to_hex(number int or bigint)
说明：Convert number to itsequivalent hexadecimal representation 　对数值进行十六进制编码
例子：to_hex(2147483647) = 7fffffff

函数：translate(string text,totext) 说明：Any character in string thatmatches a character in the from set is replaced by thecorresponding character in the to set将字符串中某些匹配的字符替换成指定字符串，目标字符与源字符都可以同时指定多个 例子：translate('12345','14','ax') = a23x5