WHERE 条件,紧跟WHERE 的user1.'user_name' IN ...... 既然是列名,目的是指明是哪一列,为什么还要加引号? 加引号不就成了 字符串了,那样为什么能识别/?
2015-10-24
If using the "is not null" rather than "is null", the right join will be same as the inner join. I think it should be "is null" in most cases.
2015-09-13