mysql - 自连接查询以获取一张表中的结果

Question

我有一个如下所示的表格。

+------+----------+--------+
|  id  |sender_id |receiver_id|
+------+----------+--------+
|  1   | 1        | 4      |
|  2   | 1        | 34     |
|  3   | 4        | 1      |
|  4   | 11       | 8      |
|  5   | 24       | 4      |
|  6   | 11       | 5      |
+------+----------+--------+

我想看到如下所示的结果。

+------+----------+--------+
|user_id|sent     |receive  |
+------+----------+--------+
|  1   | 2        | 1      |
|  4   | 1        | 2      |
|  5   | 0        | 1      |
|  8   | 0        | 1      |
| 11   | 2        | 0      |
| 24   | 1        | 0      |
| 34   | 0        | 1      |
+------+----------+--------+

我想在一张表中显示我的结果，其中一列 user_id(所有唯一的 sender_id 和receiver_id)作为 user_id，发送(count(sender_id)作为发送，count(receiver_id))作为接收。这样我就可以在一张表中获得每个用户发送和接收消息编号的结果。我正在尝试自连接查询，但没有得到我预期的结果。

Answer 1

我会使用这个查询:

SELECT user_id, SUM(sent), SUM(receive)
FROM (
  SELECT sender_id AS user_id, COUNT(*) AS sent, 0 AS receive
  FROM tablename
  GROUP BY sender_id
  UNION ALL     
  SELECT receiver_id AS user_id, 0 AS sent, COUNT(*) AS receive
  FROM tablename
  GROUP BY receiver_id
) s
GROUP BY user_id

请参阅 fiddle here .