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我的表格包含以下列：
gamelogs_id (auto_increment primary key)
player_id (int)
player_name (varchar)
game_id (int)
season_id (int)
points (int)
该表具有以下索引
+-----------------+------------+--------------------+--------------+--------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-----------------+------------+--------------------+--------------+--------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| player_gamelogs | 0 | PRIMARY | 1 | player_gamelogs_id | A | 371330 | NULL | NULL | | BTREE | | |
| player_gamelogs | 1 | player_name | 1 | player_name | A | 3375 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | points | 1 | points | A | 506 | NULL | NULL | YES | BTREE | ## Heading ##| |
| player_gamelogs | 1 | game_id | 1 | game_id | A | 37133 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | season | 1 | season | A | 30 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | team_abbreviation | 1 | team_abbreviation | A | 70 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | player_id | 1 | game_id | A | 41258 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | player_id | 2 | player_id | A | 371330 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | player_id | 3 | dk_points | A | 371330 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | game_player_season | 1 | game_id | A | 41258 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | game_player_season | 2 | player_id | A | 371330 | NULL | NULL | YES | BTREE | | |
| player_gamelogs | 1 | game_player_season | 3 | season_id | A | 371330 | NULL | NULL | | BTREE | | |
+-----------------+------------+--------------------+--------------+--------------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
我试图在比赛开始之前计算一个赛季和球员的积分平均值.因此,对于本赛季的第3场比赛,avg_points将是游戏1和2的平均值.游戏数量按顺序排列,使得较早的游戏比较晚的游戏少.我也可以选择使用日期字段,但我认为数字比较会更快？
我的查询如下：
SELECT game_id,player_id,player_name,(SELECT avg(points)
FROM player_gamelogs t2
WHERE t2.game_id < t1.game_id
AND t1.player_id = t2.player_id
AND t1.season_id = t2.season_id) AS avg_points
FROM player_gamelogs t1
ORDER BY player_name,game_id;
EXPLAIN生成以下输出：
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+-------+------+--------------------------------------+------+---------+------+--------+-------------------------------------------------+
| 1 | PRIMARY | t1 | ALL | NULL | NULL | NULL | NULL | 371330 | Using filesort |
| 2 | DEPENDENT SUBQUERY | t2 | ALL | game_id,game_player_season | NULL | NULL | NULL | 371330 | Range checked for each record (index map: 0xC8) |
我不确定这是因为涉及的任务的性质还是因为我的查询效率低下.谢谢你的任何建议！
最佳答案
请考虑以下查询：
SELECT t1.season_id,t1.game_id,t1.player_id,t1.player_name,AVG(COALESCE(t2.points,0)) AS average_player_points
FROM player_gamelogs t1
LEFT JOIN player_gamelogs t2 ON
t1.game_id > t2.game_id
AND t1.player_id = t2.player_id
AND t1.season_id = t2.season_id
GROUP BY
t1.season_id,t1.player_name
ORDER BY t1.player_name,t1.game_id;
笔记：
>要以最佳方式执行,您需要一个额外的索引(season_id,game_id,player_name)
>更好的是,将播放器表从id中检索名称.对我来说,我们必须从日志表中获取播放器名称,而且如果它在索引中是必需的,这似乎是多余的.
>按已按分组列排序已分组.如果可以,请避免事后订购,因为它会产生无用的开销.正如评论中所述,这不是一种官方行为,并且假设其随时间的一致性的结果应该考虑与突然失去分类的风险.
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