2

我有点卡住了..

我有两张桌子

mysql > EXPLAIN event;
+-------------+--------------+------+-----+---------------------+-----------------------------+
| Field       | Type         | Null | Key | Default             | Extra                       |
+-------------+--------------+------+-----+---------------------+-----------------------------+
| id          | int(11)      | NO   | PRI | NULL                | auto_increment              |
| name        | varchar(100) | NO   | MUL |                     |                             |
| extUrl      | varchar(192) | NO   |     |                     |                             |
+-------------+--------------+------+-----+---------------------+-----------------------------+

一个事件可以有多个

mysql> explain eventDate;
+----------------+--------------+------+-----+---------------------+-----------------------------+
| Field          | Type         | Null | Key | Default             | Extra                       |
+----------------+--------------+------+-----+---------------------+-----------------------------+
| id             | int(11)      | NO   | PRI | NULL                | auto_increment              |
| category_id    | int(11)      | NO   | MUL | 0                   |                             |
| event_id       | int(11)      | NO   | MUL | 0                   |                             |
| location_id    | int(11)      | NO   | MUL | 0                   |                             |
| name           | varchar(100) | NO   |     |                     |                             |
| eventDate      | timestamp    | NO   |     | 0000-00-00 00:00:00 |                             |
+----------------+--------------+------+-----+---------------------+-----------------------------+

我想通过 查询事件id，location_id下一个即将到来 eventDate的事件，我被困在如何形成该查询

我目前有这个

 SELECT
      e.id,
      d.location_id,
      d.eventDate
 FROM
      event e
          INNER JOIN eventDate d ON d.event_id = e.id AND d.eventDate >= CURRENT_TIMESTAMP
 WHERE
      e.id = 5107
 GROUP BY
      e.id
 ORDER BY
      d.eventDate ASC

现在这会返回一个结果，但是我 GROUP BY 事件，所以我不确定如何确保真的选择了下一个 eventDate。此外，我没有使用任何聚合函数（ group by one, aggregate many ），这似乎不是一个干净且明确定义的结果要求 - MySQL 现在随机选择其中一个 eventDate 行不是吗？

4

1 回答 1

2

这应该总是给你第一个即将发生的事件：

 SELECT
      e.id,
      d.location_id,
      d.eventDate
 FROM
      event e
          INNER JOIN eventDate d ON d.event_id = e.id
 WHERE
      e.id = 5107
      AND
      d.id = (SELECT d1.id FROM eventDate d1 WHERE d1.event_id = 5107 AND d1.eventDate >= CURRENT_TIMESTAMP ORDER BY d1.eventDate ASC LIMIT 1)

但更好的方法是添加LIMIT 1到您当前的查询并删除GROUP BY：

 SELECT
      e.id,
      d.location_id,
      d.eventDate
 FROM
      event e
          INNER JOIN eventDate d ON d.event_id = e.id AND d.eventDate >= CURRENT_TIMESTAMP
 WHERE
      e.id = 5107
 ORDER BY
      d.eventDate ASC
 LIMIT 1
于 2013-01-14T11:07:26.223 回答