mysql连接表与null

Question

我如何加入这两张桌子？

休息表

+----+-------------+
| id | description |
+----+-------------+
|  1 | Sample      |
|  2 | Sample 2    |
+----+-------------+

用户收藏夹

+----+---------+-----------+
| id | user_id | breaks_id |
+----+---------+-----------+
|  1 |       2 |         1 |
+----+---------+-----------+

我的预期输出

+-----------+----------+--------------+-------------+
| breaks_id | user_id  | is_favorite  | description |
+-----------+----------+--------------+-------------+
|         1 | 2        | 1            | Sample      |
|         2 | null     | null         | Sample      |
+-----------+----------+--------------+-------------+

我想查看user_id = 1的所有休息列表，如果不是收藏夹，则查看null

Answer 1

我想你只想在这里使用OUTER JOIN：

SELECT b.id AS break_id, f.user_id, f.id AS is_favorite, b.description
FROM breaks b
LEFT JOIN 
user_favorites f
ON b.id = f.breaks_id;

LEFT JOIN是一个外部联接，它将从中断表中选择所有记录，并将它们与user_favorites表中的相应条目连接起来。如果没有匹配项，相关字段将为空。

Answer 2

它会起作用

SELECT br.id AS break_id, fv.user_id, fv.id AS is_favorite,
 br.description
 from breaks br
 left join  favorites fv
 on br.id = fv.id
 where fv.id is null;