SQL> select * from test where username is null;USERNAME USERNUM -------------------- --------------------------------------- 234SQL> select * from test where username ='';USERNAME USERNUM -------------------- ---------------------------------------SQL> select * from test where username=' ';USERNAME USERNUM -------------------- --------------------------------------- 在oracle 中判断为空就用is null;
估计楼上是没有看明白楼主的意思吧,楼上是说 left join 结果会因为右边链接条件不一致而改变。。但是我没有模拟出来楼主的情况,看是不是什么地方敲错了。。
SQL> select * from test where username is null;USERNAME USERNUM
-------------------- ---------------------------------------
234SQL> select * from test where username ='';USERNAME USERNUM
-------------------- ---------------------------------------SQL> select * from test where username=' ';USERNAME USERNUM
-------------------- ---------------------------------------
在oracle 中判断为空就用is null;