ltrim(x,y) 函數(shù)是按照y中的字符一個一個截掉x中的字符，并且是從左邊開始執(zhí)行的，只要遇到y(tǒng)中有的字符，x中的字符都會被截掉，直到在x的字符中遇到y(tǒng)中沒有的字符為止函數(shù)命令才結(jié)束 。

參閱Oracle? Database SQL Reference

10g Release 2 (10.2)

Part Number B14200-02

中所說的

LTRIM的原型是LTRIM(char [, set ])

LTRIM removes from the left end of char all of the characters contained in set. If you do not specify set, it defaults to a single blank. If char is a character literal, then you must enclose it in single quotes. Oracle Database begins scanning char from its first character and removes all characters that appear in set until reaching a character not in set and then returns the result.

LTRIM函數(shù)的第二個參數(shù)實際上是個集合，Oracle數(shù)據(jù)庫會從char的第一個字符開始掃描，移除掉set集合中出現(xiàn)的字符，直到遇到一個不在set集合中的字符為止。