Multiple SELECT with NOT IN - inner SELECT语句返回空，整个SELECT返回空

Question

有两个表TABLE1和TABLE2，其中有一个公共字段ID。我想根据ID值从TABLE2中检索与TABLE1不匹配的值。

select * from TABLE2 where subject = 1 and ID NOT IN (select ID from TABLE1 where subject = 1)

示例:

TABLE1
ID SUBJECT
1 1

TABLE2
ID SUBJECT
1 1
2 1

预期结果是2，并且运行良好。

但是当TABLE1为空或者内部 select ID from TABLE1 where subject = 1返回空时，整个select语句返回空。但是预期的结果是1,2

有没有办法做到这一点?

Answer 1

使用left join

select t2.* 
from table2 t2
left outer join table1 t1 on t1.id = t2.id and t1.subject = 1
where t2.subject = 1
and t1.id is null

查看连接的详细说明

Answer 2

我认为你也可以使用非exists -

select * from TABLE2 where subject = 1 and NOT exists
(select 1 from TABLE1 where subject = 1 and table1.id = table2.id)