[英]Querying many-to-many relationship in MySql
可以說我們有這個表a_b,它與表a和b是多對多關系:
+------+------+
| a_id | b_id |
+------+------+
| 1 | 1 |
| 1 | 2 |
| 1 | 3 |
| 2 | 1 |
| 2 | 2 |
+------+------+
現在,我想查詢該表,以便獲得所有a_id,其中包含b_id(1、2、3)的條目。 在上面的示例中,輸出應為
+------+
| a_id |
+------+
| 1 |
+------+
原因a_id = 2
沒有b_id = 3
條目
一種可能的查詢是:
select *
from a
join a_b as a_b1
on a_b1.a_id = a.id and a_b1.b_id = 1
join a_b as a_b2
on a_b2.a_id = a.id and a_b2.b_id = 2
join a_b as a_b3
on a_b3.a_id = a.id and a_b3.b_id = 3
但是... naaaa ...
解決此問題的更好方法是什么?
我認為更簡單的方法是按group by
並having
:
select a_id
from a_b
where b_id in (1, 2, 3)
group by a_id
having count(*) = 3;
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