连接三个表A、B、C并返回mysql中A中的common

Question

I want to join below three tables A, B, C and return only common(shaded) part of table A

A
-------
ID, Name

B
-------
ID, ORG

C
--------
ID, DEP

Please anyone provide simple join query

Answer 1

I understand that you want rows from a whose id can be foud in either b or c .

This sounds like two exists subquery:

select a.*
from a
where 
    exists (select 1 from b where b.id = a.id)
    or exists (select 1 from c where c.id = a.id)

If you also want columns from tables b or c, you can use two left joins instead, with a where condition that ensures that at least one of the joins did succeed:

select a.*, b.org, c.dept
from a
left join b on b.id = a.id
left join c on c.id = a.id
where b.id is not null or c.id is not null

Answer 2

You want a left join starting with A and then some filtering:

select . . .
from a left join
     b
     on . . .  left join
     c
     on . . .
where b.? is not null or c.? is not null;

The ? are either columns used in the join s or primary keys on the respective tables.