在oracle中，trim()函数的用法有,leading 开头字符，trailing 结尾字符，both 开头和结尾字符，如下：
trim(leading || trailing || both '将要被替换掉的字符" from “将要被替换的字符串")
1、trim函数去除指定的开头字符
select trim(leading 'x' from 'xday') as strTemp from tableName ;
2、trim函数去除指定的结尾字符
select trim(trailing 'x' from 'dayx') as strTemp from tableName ;
3、trim函数去除指定的首部和尾部字符
select trim(both 'x' from 'xdayx') as strTemp from tableName ;
4、默认情况下，trim函数会去除首部和尾部，被指定的字符
select trim('x' from 'xdayx') as strTemp from tableName ;
5、如果没有指定被移除的字符，则会默认去除首部和尾部的空格
select trim(' day ') as strTemp from tableName ;