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) or character_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 [for int])
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 in string)
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] [for int])
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
from pattern)
说明：Extract substring matching POSIX regular expression. See Section
9.7 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
for escape)
说明：Extract substring matching SQL regular expression. See Section
9.7 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 (a
space 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 UTF8
returns the
Unicode code point
of the
character.
For other multibyte encodings. the argument must be a strictly
ASCII character. 得到某一个字符的Assii值
例子：ascii(
'x')
= 120
函数：btrim(string text [, characters text])
说明：Remove the longest string consisting only of characters
in characters (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 treated
as a
Unicode code point.
For other multibyte encodings the argument must designate a strictly
ASCII character. The
NULL (
0)
character is 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
to dest_encoding. The original encoding
is specified
by src_encoding. The string must be valid
in this encoding. Conversions can be defined
by CREATE CONVERSION. Also there are
some predefined conversions. 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_utf8 represented
in ISO
8859-1 encoding
函数：convert_from(string bytea, src_encoding name)
说明：Convert string
to the
database encoding. The original encoding
is specified
by src_encoding. The string 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 represented
in the
current database encoding
函数：convert_to(string text, dest_encoding name)
说明：Convert string
to dest_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 the UTF8 encoding
函数：decode(string text, type
text)
说明：Decode binary data
from string previously encoded
with encode. Parameter type
is same
as in encode. 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, type text)
说明：Encode binary data
to different 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
of each word
to uppercase
and the rest
to lowercase. Words are sequences
of alphanumeric characters separated
by non
-alphanumeric characters. 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 of characters
in string
in the given encoding. The string must be valid
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 [, fill text])
说明：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). 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 [, characters text])
说明：Remove the longest string containing 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 of string, 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 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. 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 string suitably quoted
to be used
as a string literal
in an SQL statement string. Embedded
single-quotes
and backslashes are properly doubled. 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 text and then quote it as a literal. Embedded single-quotes and backslashes 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：Return all captured substrings resulting from matching a POSIX regular expression against the string. See Section 9.7.3 for more information. 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) matching a 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, pattern text [, flags text ])
说明：Split string using a POSIX regular expression as the delimiter. See Section 9.7.3 for more information. 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, pattern text [, flags text])
说明：Split string using a POSIX regular expression as the delimiter. See Section 9.7.3 for more information. 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 specified number 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, to text)
说明：Replace all occurrences 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, length int [, fill text])
说明：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. 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(string text [, characters text])
说明：Remove the longest string containing only characters from characters (a space by 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：Split string 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 specified substring (same as position(substring in string), but note the reversed 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 as substring(string from from for count)) 截取子串
例子：substr('alphabet
', 3, 2) = ph
函数：to_ascii(string text [, encoding text])
说明：Convert string to ASCII from another encoding (only supports conversion from LATIN1, 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 its equivalent hexadecimal representation 对数值进行十六进制编码
例子：to_hex(2147483647) = 7fffffff
函数：translate(string text, from text, to text)
说明：Any character in string that matches a character in the from set is replaced by the corresponding 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
转载于:https://www.cnblogs.com/ssqhan/p/7284087.html
