我正在尝试(并且失败)加入SQLite数据库中的一些表。数据本身很复杂,但我想我已经把它归结为一个说明性的例子。
这是我要加入的三个表。
表:事件
+----+---------+-------+-----------+
| id | user_id | class | timestamp |
+----+---------+-------+-----------+
| 1 | 'user1' | 6 | 100 |
| 2 | 'user1' | 12 | 400 |
| 3 | 'user1' | 4 | 900 |
| 4 | 'user2' | 6 | 400 |
| 5 | 'user2' | 3 | 800 |
| 6 | 'user2' | 8 | 900 |
+----+---------+-------+-----------+
表:游戏
+---------+---------+------------+-----------+
| user_id | game_id | game_class | timestamp |
+---------+---------+------------+-----------+
| 'user1' | 1 | 'A' | 200 |
| 'user2' | 2 | 'A' | 300 |
| 'user1' | 3 | 'B' | 500 |
| 'user1' | 4 | 'A' | 600 |
| 'user1' | 5 | 'A' | 700 |
+---------+---------+------------+-----------+
表:分数
+---------+-------+
| game_id | score |
+---------+-------+
| 1 | 8 |
| 2 | 2 |
| 4 | 9 |
| 5 | 6 |
+---------+-------+
我想加入这些内容,在第一个表格中提供一个附加列,其中包含活动时游戏类A中用户的当前得分。即我希望联接的结果看起来像这样:
期望的结果
+----+----------+-------+-----------+-----------------+
| id | user_id | class | timestamp | current_a_score |
+----+----------+-------+-----------+-----------------+
| 1 | 'user1' | 6 | 100 | (null) |
| 2 | 'user1' | 12 | 400 | 8 |
| 3 | 'user1' | 4 | 900 | 6 |
| 4 | 'user2' | 6 | 400 | 2 |
| 5 | 'user2' | 3 | 800 | 2 |
| 6 | 'user2' | 8 | 900 | 2 |
+----+----------+-------+-----------+-----------------+
以下简单连接汇总了两个表AScores和Games。
SELECT * FROM AScores
INNER JOIN Games
ON AScores.game_id = Games.game_id
所以我希望将它作为子查询加入到Events表中。像这样的东西:
SELECT Events.*, AScoredGames.time_stamp AS game_time_stamp, AScoredGames.score
FROM Events
LEFT OUTER JOIN (
SELECT AScores.score, Games.* FROM AScores
INNER JOIN Games
ON AScores.game_id = Games.game_id
) AS AScoredGames
ON Events.user_id = AScoredGames.user_id
AND Events.time_stamp >= AScoredGames.time_stamp
ORDER BY Events.time_stamp ASC
这导致以下结果:
+----+---------+-------+------------+-----------------+-------+
| id | user_id | class | time_stamp | game_time_stamp | score |
+----+---------+-------+------------+-----------------+-------+
| 1 | user1 | 6 | 100 | NULL | NULL |
| 2 | user1 | 12 | 400 | 200 | 8 |
| 4 | user2 | 6 | 400 | 300 | 2 |
| 5 | user2 | 3 | 800 | 300 | 2 |
| 6 | user2 | 8 | 900 | 300 | 2 |
| 3 | user1 | 4 | 900 | 200 | 8 |
| 3 | user1 | 4 | 900 | 600 | 9 |
| 3 | user1 | 4 | 900 | 700 | 6 |
+----+---------+-------+------------+-----------------+-------+
因此,我需要通过Events.id进行分组,以使用Events.id 3来删除三重行。但我想要做的是选择具有最大game_time_stamp的行,然后使用行的分数。如果我做MAX(game_time_stamp)作为我的聚合,我仍然必须独立地聚合得分。有没有办法将得分列的聚合函数中的行选择与game_time_stamp列的聚合函数的结果联系起来?
(NB Select first record in a One-to-Many relation using left join和SQL Server: How to Join to first row等问题的现有答案似乎表明我不能并且说必须在子查询中使用WHERE子句。但是我正在努力解决这个问题(我会发布另一个问题)我可以想到至少有一个解决方案,我希望有更好的解决方案。)
以下查询应该这样做。它使用带有相关子查询的NOT EXISTS
条件来定位每个事件的相关游戏记录。
SELECT e.*, s.score current_a_score
FROM
events e
LEFT JOIN games g
ON g.user_id = e .user_id
AND g.timestamp < e.timestamp
AND NOT EXISTS (
SELECT 1
FROM games g1
WHERE
g1.user_id = e .user_id
AND g1.timestamp < e.timestamp
AND g1.timestamp > g.timestamp
)
LEFT JOIN ascores s
ON s.game_id = g.game_id
ORDER BY e.id
这个带有测试数据的DB Fiddle demo返回:
| id | user_id | class | timestamp | current_a_score |
| --- | ------- | ----- | --------- | --------------- |
| 1 | user1 | 6 | 100 | |
| 2 | user1 | 12 | 400 | 8 |
| 3 | user1 | 4 | 900 | 6 |
| 4 | user2 | 6 | 400 | 2 |
| 5 | user2 | 3 | 800 | 2 |
| 6 | user2 | 8 | 900 | 2 |
我有一个解决方法,但它感觉hacky并依赖于我的数据的细节。首先请注意,time_stamps都是100的倍数,而得分都低于10.我可以用不会干扰我的比较的方式对它们进行组合,但这意味着它们都在一个数字列中编码。此查询提供了所需的结果:
SELECT Events.id, MIN(Events.user_id) AS user_id, MIN(Events.class) AS class, MIN(Events.time_stamp) AS time_stamp, MAX(AScoredGames.combination) % 10 AS current_a_score
FROM Events
LEFT OUTER JOIN (
SELECT AScores.score, AScores.score + (Games.time_stamp - 10) AS combination, Games.* FROM AScores
INNER JOIN Games
ON AScores.game_id = Games.game_id) AS AScoredGames
ON Events.user_id = AScoredGames.user_id AND Events.time_stamp >= AScoredGames.time_stamp
GROUP BY Events.id
ORDER BY id ASC
(组合在AScores.score + (Games.time_stamp - 10)
完成,因此聚合函数变为MAX(AScoredGames.combination) % 10
。)
实际结果
+----+---------+-------+------------+-----------------+
| id | user_id | class | time_stamp | current_a_score |
+----+---------+-------+------------+-----------------+
| 1 | user1 | 6 | 100 | NULL |
| 2 | user1 | 12 | 400 | 8 |
| 3 | user1 | 4 | 900 | 6 |
| 4 | user2 | 6 | 400 | 2 |
| 5 | user2 | 3 | 800 | 2 |
| 6 | user2 | 8 | 900 | 2 |
+----+---------+-------+------------+-----------------+