Question

我有两个桌子

 myexercise
 id | ex_name | ex_id | owner_id
 1   exercise1    2        1
 2   exercise2    3        1

和

exercise
id | ex_name
 2   exercise1
 3   exercise2
 4   exercise3

我想编写SQL查询，该查询仅返回EXERCISE TABLE中的行，其中id不作为ex_id出现在MYEXERCISE表中。因此，它应该仅返回id => 4和ex_name => exercise3。我认为可以使用JOINS来完成，但是我不知道如何。

Answer 1

您可以使用where not exists

select t1.*
from Exercise t1
where not exists (select 1 from MyExercise t2 where t1.ex_id = t2.id)

或者是join

select t1.*
from Exercise t1
left join MyExercise t2
  on t1.ex_id = t2.id
where t2.id is null

Answer 2

您可以按以下方式尝试LEFT JOIN：

    Select *
    from EXERCISE e left join MYEXERCISE me
    ON e.id = ME.id
    Where me.id IS NULL;

Answer 3

select * from Exercise
where id not in (select ex_id from myExercise);

select * from Exercise t1
where not exists (select * from myExercise t2 where t1.Id = t2.ex_id);

select * from Exercise t1
left join MyExercise t2 on t1.Id = t2.ex_id
where myExercise.ex_id is null;

所有这3个查询都会做到这一点。

如何查询数据库以不返回满足条件的行

3 个答案: