[英]Update mySQL Table with Results of Aggregate Function
我有一个汇总表和一个详细表,其中包含许多不同游戏的得分。 详细信息表包含数百万条记录,汇总表仅包含每个游戏和不同天数的平均得分。
例:
汇总表:
| ID | Name | AVG_SCORE_7_DAYS | AVG_SCORE_30_DAYS | ----------------------------------------------------- | 1 | Game 1| 10.3 | 20.3 | | 2 | Game 2| 14.3 | 26.3 |
明细表:
| ID | Name | Date | Score | -------------------------------------------- | 1 | Game 1| 2015-07-12 01:00:00 | 20 | | 2 | Game 2| 2015-07-12 01:00:00 | 26 | | 3 | Game 1| 2015-07-12 01:00:00 | 14 | | 4 | Game 2| 2015-07-12 01:00:00 | 9 |
我使用如下代码通过存储过程每晚更新我的聚合表:
UPDATE `aggregate` aggr
INNER JOIN
(
SELECT game_name, avg(score) AS avg_score
FROM `detail`
WHERE `date` BETWEEN (CURDATE() + INTERVAL -7 DAY) AND CURDATE()
GROUP BY `game_name`
) detail7 ON aggr.`game_name` = detail7.`game_name`
INNER JOIN
(
SELECT game_name, avg(score) AS avg_score
FROM `detail`
WHERE `date` BETWEEN (CURDATE() + INTERVAL -30 DAY) AND CURDATE()
GROUP BY `game_name`
) detail30 ON aggr.`game_name` = detail30.`game_name`
我的问题是,如果在7天,30天等时间内某些游戏没有得分,那么这些子查询将不返回任何记录,因此,如果其中任何一个失败,则该游戏的所有列都不会更新(由于内部联接)。 有没有一种方法可以编写我的查询来更新其他列,即使子查询的结果不返回任何结果呢?
使用外部联接。 您还可以简化逻辑,因此仅需要一种聚合:
UPDATE `aggregate` aggr LEFT JOIN
(SELECT game_name,
avg(case when `date` BETWEEN (CURDATE() + INTERVAL -7 DAY) AND CURDATE() then score end) AS avg_score_07,
avg(case when `date` BETWEEN (CURDATE() + INTERVAL -30 DAY) AND CURDATE() then score end) AS avg_score_30
FROM `detail`
WHERE `date` BETWEEN (CURDATE() + INTERVAL -30 DAY) AND CURDATE()
GROUP BY `game_name`
) detail
ON aggr.`game_name` = detail.`game_name`
SET . . . ;
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