mysql - MySQL 使用 Count 连接查询

Question

我有 2 张桌子，EVENT并且EVENT_INVITATION. 我想选择所有事件：

EVENT.creator_id = x
OR
EVENT_INVITATION.invitee_id = x

但我还需要返回EVENT_INVITATION每个结果的总行数EVENT。

Answer 1

我认为这会做到：

SELECT count(*), EVENT.event_id
FROM EVENT, 
EVENT_INVITATION, 
(
  SELECT event_ID
  FROM EVENT
  WHERE creator_id = x
  UNION
  SELECT event_id
  FROM EVENT_INVITATION.
  WHERE invitee_id = x) temp
WHERE EVENT.event_ID = EVENT_INVITATION.event_ID
AND EVENT.event_ID = temp.event_ID
GROUP BY EVENT.event_id

我建议在没有你的数据结构和样本集的情况下做一个sql fiddle原因，我无法测试它。

Answer 2

获取您关心的所有事件的列表，然后计算相关的邀请。在没有邀请的情况下外部加入。

WITH selectEvents AS (
    SELECT event_id
      FROM event
      WHERE creator_id = <x>
    UNION
    SELECT event_id
      FROM event_invitation
      WHERE invitee_id = <x>
)
SELECT s.event_id, COUNT(i.event_id) AS theCount
  FROM selectEvents s
  LEFT OUTER JOIN event_invitation i ON (i.event_id = s.event_id)
  GROUP BY s.event_id