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：select '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：select bit_length('pmars') = 40

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：select char_length('pmars'); = 5

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函数：lower(string)

说明：Convert string to lower case 转换字符串为小写

例子：select lower('PmArS'); = "pmars"

函数：octet_length(string)

说明：Number of bytes in string 计算字符串的字节数

例子：select octet_length('我是pmars'); = 11 select octet_length('我'); = 3

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：select overlay('I am pmars' placing 'ming' from 6 for 5); = "I am ming"

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：select position('ma' in 'pmars'); = 2

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：select substring('topmars' from 3 for 3); = "pma"

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：select substring('topmars' from 'p.*$'); = "pmars"

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：select substring('Thomas' from '%#"o_a#"_' for '#'); = "oma"

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：select trim(leading 'p' from 'pmars'); = "mars"

函数：upper(string)

说明：Convert string to uppercase 将字符串转换为大写 www.2cto.com

例子：select upper('pmars'); = "PMARS"

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：select ascii('pmars'); = select ascii('p'); = 112

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：select btrim('pmars','prs'); = "ma"

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：select chr(65); = A

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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