oracle中not in可以这样用不?
select * from course where precourseid not in (select precourseid from course where precourseid is not null);
子查询会返回四个id数字值,我想查询precourseid为null的行的所有信息,如果直接查询select * from course where precourseid is null;这样会得到想要的结果,但是如果用子查询那样就会出错,求解答。