函数：chr(int)说明：Characterwiththegivencode.ForUTF8theargumentistreatedasaUnicodecodepoint.ForothermultibyteencodingstheargumentmustdesignateastrictlyASCIIcharacter.TheNULL(0)characterisnotallowedbecausetextdatatypescannotstoresuchbytes.得到某ACSII值对应的字符例子：chr(65)=A

函数：convert(stringbytea,src_encodingname,dest_encodingname)说明：Convertstringtodest_encoding.Theoriginalencodingisspecifiedbysrc_encoding.Thestringmustbevalidinthisencoding.ConversionscanbedefinedbyCREATECONVERSION.Alsotherearesomepredefinedconversions.SeeTable9-7foravailableconversions.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_utf8representedinISO8859-1encoding

函数：convert_from(stringbytea,src_encodingname)说明：Convertstringtothedatabaseencoding.Theoriginalencodingisspecifiedbysrc_encoding.Thestringmustbevalidinthisencoding.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_utf8representedinthecurrentdatabaseencoding

函数：convert_to(stringtext,dest_encodingname)说明：Convertstringtodest_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('sometext','UTF8')=sometextrepresentedintheUTF8encoding

函数：decode(stringtext,typetext)说明：Decodebinarydatafromstringpreviouslyencodedwithencode.Parametertypeissameasinencode.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(databytea,typetext)说明：Encodebinarydatatodifferentrepresentation.Supportedtypesare:base64,hex,escape.Escapemerelyoutputsnullbytesas\000anddoublesbackslashes.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：Convertthefirstletterofeachwordtouppercaseandtheresttolowercase.Wordsaresequencesofalphanumericcharactersseparatedbynon-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('hiTHOMAS')=HiThomas

函数：length(string)说明：Numberofcharactersinstring讲算字符串长度例子：length('jose')=4

函数：length(stringbytea,encodingname)说明：Numberofcharactersinstringinthegivenencoding.Thestringmustbevalidinthisencoding.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(stringtext,lengthint[,filltext])说明：Fillupthestringtolengthlengthbyprependingthecharactersfill(aspacebydefault).Ifthestringisalreadylongerthanlengththenitistruncated(ontheright).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(stringtext[,characterstext])说明：Removethelongeststringcontainingonlycharactersfromcharacters(aspacebydefault)fromthestartofstring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：CalculatestheMD5hashofstring,returningtheresultinhexadecimal将字符串进行md5编码例子：md5('abc')=900150983cd24fb0d6963f7d28e17f72

*函数：pg_client_encoding()说明：Currentclientencodingname得到pg客户端编码例子：pg_client_encoding()=SQL_ASCII

*函数：quote_ident(stringtext)说明：ReturnthegivenstringsuitablyquotedtobeusedasanidentifierinanSQLstatementstring.Quotesareaddedonlyifnecessary(i.e.,ifthestringcontainsnon-identifiercharactersorwouldbecase-folded).Embeddedquotesareproperlydoubled.对某一字符串加上两引号例子：quote_ident('Foobar')="Foobar"

*函数：quote_literal(stringtext)说明：ReturnthegivenstringsuitablyquotedtobeusedasastringliteralinanSQLstatementstring.Embeddedsingle-quotesandbackslashesareproperlydoubled.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：regexp_matches(stringtext,patterntext[,flagstext])说明：ReturnallcapturedsubstringsresultingfrommatchingaPOSIXregularexpressionagainstthestring.SeeSection9.7.3formoreinformation.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(stringtext,patterntext,replacementtext[,flagstext])说明：Replacesubstring(s)matchingaPOSIXregularexpression.SeeSection9.7.3formoreinformation.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(stringtext,patterntext[,flagstext])说明：SplitstringusingaPOSIXregularexpressionasthedelimiter.SeeSection9.7.3formoreinformation.利用正则表达式将字符串分割成数组例子：regexp_split_to_array('helloworld',E'\\s+')={hello,world}

*函数：regexp_split_to_table(stringtext,patterntext[,flagstext])说明：SplitstringusingaPOSIXregularexpressionasthedelimiter.SeeSection9.7.3formoreinformation.利用正则表达式将字符串分割成表格例子：regexp_split_to_table('helloworld',E'\\s+')=helloworld(2rows)

*函数：repeat(stringtext,numberint)说明：Repeatstringthespecifiednumberoftimes重复字符串一指定次数例子：repeat('Pg',4)=PgPgPgPg

函数：replace(stringtext,fromtext,totext)说明：Replacealloccurrencesinstringofsubstringfromwithsubstringto将字符的某一子串替换成另一子串例子：('abcdefabcdef','cd','XX')=abXXefabXXef

selectoverlay('http://tp2.sinaimg.cn/1928431341/50/5621497131/1'placing'/180/'fromposition('/50/'in'http://tp2.sinaimg.cn/1928431341/50/5621497131/1')for4),replace('http://tp2.sinaimg.cn/1928431341/50/5621497131/1','/50/','/180/');

*函数：rpad(stringtext,lengthint[,filltext])说明：Fillupthestringtolengthlengthbyappendingthecharactersfill(aspacebydefault).Ifthestringisalreadylongerthanlengththenitistruncated.对字符串进行填充，填充内容为指定的字符串例子：rpad('hi',5,'xy')=hixyx

函数：rtrim(stringtext[,characterstext])说明：Removethelongeststringcontainingonlycharactersfromcharacters(aspacebydefault)fromtheendofstring去除字符串右边指定的字符例子：rtrim('trimxxxx','x')=trim

*函数：split_part(stringtext,delimitertext,fieldint)说明：Splitstringondelimiterandreturnthegivenfield(countingfromone)?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：Locationofspecifiedsubstring(sameasposition(substringinstring),butnotethereversedargumentorder)指定字符串在目标字符串的位置例子：strpos('high','ig')=2

selectstrpos('http://tp2.sinaimg.cn/1928431341/50/5621497131/1','/50/'),position('/50/'in'http://tp2.sinaimg.cn/1928431341/50/5621497131/1');

函数：substr(string,from[,count])说明：Extractsubstring(sameassubstring(stringfromfromforcount))截取子串例子：substr('alphabet',3,2)=ph

*函数：to_ascii(stringtext[,encodingtext])说明：ConvertstringtoASCIIfromanotherencoding(onlysupportsconversionfromLATIN1,LATIN2,LATIN9,andWIN1250encodings)将字符串转换成ascii编码字符串例子：to_ascii('Karel')=Karel

*函数：to_hex(numberintorbigint)说明：Convertnumbertoitsequivalenthexadecimalrepresentation　对数值进行十六进制编码例子：to_hex(2147483647)=7fffffff

*函数：translate(stringtext,fromtext,totext)说明：Anycharacterinstringthatmatchesacharacterinthefromsetisreplacedbythecorrespondingcharacterinthetoset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