意外结果：如果 tblA.ID 与 tblB.ID 不匹配，则查询以显示 tblA 记录

Question

I made a query to show tblA records if tblA.ID doesn't match tblB.ID. The query works fine only if there is at least one record in tblB, but if tblB has no records then the query of tblA will return empty, though tblA should return all its records. Below is the code with the unexpected result:

SELECT tblA.id
FROM tblA INNER JOIN tblB ON tblA.id = tblB.id;

The Unexpected result also occurs in this format:

SELECT *
FROM tblA , tblB 
WHERE tblA .id Not Like tblB .id;

Example of the desired an undesired results:

Answer 1

In your case Left join should be used. Try it.

select tbl1.Id
from tbl1 
left join tbl2 on tbl1.Id = tbl2.Id
where tbl2.Id is null

Answer 2

select * from tblA where id in (select id from tblA 除了 select id from tblB )