合并两个内部联接？

Question

我有以下表格：

dealer
    id (PK)
car
    - id (PK)
    - dealer_id (FK)
notes
    - car_id (FK)
    - dealer_id (FK)
    - user_id (FK)
    - is_active Bool

我希望能够 select 所有我有活跃票据的经销商。 当前型号不存储dealer_id在笔记上car_id 一次记笔记。这是一个非此即彼.

我可以单独查询：

select *
from dealer
inner join notes n on dealer.id = n.dealer_id and n.user_id=${userId} and n.is_active=true

和：

select *
from dealer
inner join car c on dealer.id = c.dealer_id
inner join notes n on c.id = n.car_id and n.user_id=${userId} and n.is_active=true

我试图在查询中简单地组合两个内部联接，但随后：

inner join car c on dealer.id = c.dealer_id

会筛选出第一个查询会给我什么，所以我不会得到我应该得到的所有经销商。

如何编写一个查询来提供我拥有有效备注的所有经销商？我不想在结果中出现重复的经销商。

Answer 1

你快到了。你要的叫UNION:

SELECT n.*
FROM
    notes AS n
    INNER JOIN dealer AS d ON d.id = n.dealer_id
UNION
SELECT n.*
FROM
    notes AS n
    INNER JOIN car AS c ON c.id = n.car_id
    INNER JOIN dealer AS d ON d.id = c.dealer_id

合并两个内部联接？

Combine two inner joins?

postgresql

inner-join