SQL连接查询 [英] SQL join query

问题描述

选择*来自emp1

select * from emp2



select * from emp2 as e

其中名字不在（从emp1中选择名称，其中id = e.id）

select * from emp1
select * from emp2

select * from emp2 as e
where name not in (select name from emp1 where id=e.id)

id  name
5   4444
5   5555
5   2222
5   7777

id  name
5   1111
5   7777
6   4444

id  name
5   1111
6   4444

Ab ove查询结果如下。但最后我们想通过join获得第3个结果集。但是第3个结果集通过Co相关查询发生

Above Query result are following. but finally we want 3rd result set by join.but this 3rd result set happens through Co-related query

推荐答案

你需要使用LEFT JOIN来实现它

You need to use LEFT JOIN for it

select emp2.* 
from emp2 LEFT JOIN emp1 ON emp1.id=emp2.id and emp1.name=emp2.name 
where emp1.name IS NULL

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