Question

假设我有一张这样的表：

+---------+------------------+
| post_id | original_post_id |
+---------+------------------+
| 1       | 0                |
| 2       | 0                |
| 3       | 0                |
| 4       | 2                |
| 5       | 2                |
| 6       | 0                |
| 7       | 1                |
| 8       | 1                |
| 9       | 1                |
| 10      | 0                |
| 11      | 0                |
| 12      | 3                |
+---------+------------------+

简而言之，在此表中我包含用户帖子，我想展示类似时间轴的内容。所有具有original_post_id=0的记录都是原始帖子，并且必须在任何情况下显示。但所有带original_post_id!=0的记录都是重新发布的，所以我想只展示一次。所以，结果，我需要这样的东西：

+---------+------------------+
| post_id | original_post_id |
+---------+------------------+
| 1       | 0                |
| 2       | 0                |
| 3       | 0                |
| 4       | 2                |
| 6       | 0                |
| 7       | 1                |
| 10      | 0                |
| 11      | 0                |
| 12      | 3                |
+---------+------------------+

据我了解，我必须使用GROUP BY，但具体如何？

Answer 1

您可以使用单个group by执行此操作，但这很棘手：

select min(post_id) as post_id, min(original_post_id)
from t
group by original_post_id,
         (case when original_post_id = 0 then post_id end);

Answer 2

你可以试试这个：

SELECT * FROM tableName
Where original_post_id = 0
Union
SELECT * FROM tableName
Where original_post_id != 0
Group by original_post_id

MySQL查询中的GROUP BY

2 个答案: