ORACLE TRIM

In Oracle/PLSQL, the trim function removes all specified characters either from the beginning or the ending of a string.

The syntax for the trim function is:

trim( [ leading | trailing | both  [ trim_character ]  ]   string1 )

leading - remove trim_string from the front of string1.

trailing - remove trim_string from the end of string1.

both - remove trim_string from the front and end of string1.

If none of these are chosen (ie: leading, trailing, both), the trim function will remove trim_string from both the front and end of string1.

trim_character is the character that will be removed from string1. If this parameter is omitted, the trim function will remove all leading and trailing spaces from string1.

string1 is the string to trim.

trim('   tech   ')
would return 'tech'

trim(' '  from  '   tech   ')
would return 'tech'

trim(leading '0' from '000123')
would return '123'

trim(trailing '1' from 'Tech1')
would return 'Tech'

trim(both '1' from '123Tech111')
would return '23Tech'

注:截取集只能有一个字符.

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另外找到关于ltrim(str [,set])和rtrim(str [,set])的示例:
例一:select ltrim('109224323','109') from dual;     //224323

例二:SQL> select ltrim('10900094323','109') from dual;    //4323

例三:SQL> select ltrim('10900111000991110224323','109') from dual;  //224323

例四:SQL> select ltrim('109200111000991110224323','109') from dual;  //200111000991110224323

例五:SQL> select ltrim('902100111000991110224323','109') from dual;  //2100111000991110224323

总结：ltrim(x,y) 函数是按照y中的字符一个一个截掉x中的字符，并且是从左边开始执行的，只要遇到y中有的字符, x中的字符都会被截掉, 直到在x的字符中遇到y中没有的字符为止函数命令才结束 .