Question

一个“普通SQL问题”：）我有两个表，第三个表充当“半连接表”，这意味着有时两个外键中只有一个。。有办法加入他们吗？

例如，给定以下数据：

Table D id s: 1,2,3,4,5
Table C id s: 1,2,3
Table Junction (D.id, C.id): (1,1) (2, NULL) (3, NULL) (4,2) (5,3)

is there a way to retrieve the following?
([D fields of row id 1], [C fields of row id 1])
([D fields of row id 2], [NULL C fields])
([D fields of row id 3], [NULL C fields])
([D fields of row id 4], [C fields of row id 2])
([D fields of row id 5], [C fields of row id 3])

If it s relevant, I m using PostgreSQL.
Thanks for your time!

Answer 1

SELECT  d.*, c.*
FROM    d
JOIN    junction j
ON      j.d_id = d.id
LEFT JOIN
        с
ON      c.id = j.c_id

友情链接