[英]Possible to improve the performance of this SQL query?
我有一个具有超过100,000,000行的表,并且我有一个查询,如下所示:
SELECT
COUNT(IF(created_at >= '2015-07-01 00:00:00', 1, null)) AS 'monthly',
COUNT(IF(created_at >= '2015-07-26 00:00:00', 1, null)) AS 'weekly',
COUNT(IF(created_at >= '2015-06-30 07:57:56', 1, null)) AS '30day',
COUNT(IF(created_at >= '2015-07-29 17:03:44', 1, null)) AS 'recent'
FROM
items
WHERE
user_id = 123456;
该表如下所示:
CREATE TABLE `items` (
`user_id` int(11) NOT NULL,
`item_id` int(11) NOT NULL,
`created_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00',
PRIMARY KEY (`user_id`,`item_id`),
KEY `user_id` (`user_id`,`created_at`),
KEY `created_at` (`created_at`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
解释看起来相当无害,减去了大量的行数:
1 SIMPLE items ref PRIMARY,user_id user_id 4 const 559864 Using index
我使用查询在4个时间段内收集特定用户的计数。 有没有一种更聪明/更快的方法来获取相同的数据,或者我是将新行放入此表时对这些数据进行计数的唯一选择吗?
如果您在created_at上有索引,我还将在where子句created_at> ='2015-06-30 07:57:56'中输入,这是您细分中的最低日期。
同样,对于相同的索引,它可能会拆分为4个查询:
select count(*) AS '30day'
FROM
items
WHERE
user_id = 123456
and created_at >= '2015-06-30 07:57:56'
union ....
等等
我会在created_at字段上添加索引:
ALTER TABLE items ADD INDEX idx_created_at (created_at)
或(按照托马斯的建议),因为您还要过滤user_id的created_at和user_id复合索引:
ALTER TABLE items ADD INDEX idx_user_created_at (user_id, created_at)
然后将您的查询写为:
SELECT 'monthly' as description, COUNT(*) AS cnt FROM items
WHERE created_at >= '2015-07-01 00:00:00' AND user_id = 123456
UNION ALL
SELECT 'weekly' as description, COUNT(*) AS cnt FROM items
WHERE created_at >= '2015-07-26 00:00:00' AND user_id = 123456
UNION ALL
SELECT '30day' as description, COUNT(*) AS cnt FROM items
WHERE created_at >= '2015-06-30 07:57:56' AND user_id = 123456
UNION ALL
SELECT 'recent' as description, COUNT(*) AS cnt FROM items
WHERE created_at >= '2015-07-29 17:03:44' AND user_id = 123456
是的,输出有些不同。 或者您可以使用内联查询:
SELECT
(SELECT COUNT(*) FROM items WHERE created_at>=... AND user_id=...) AS 'monthly',
(SELECT COUNT(*) FROM items WHERE created_at>=... AND user_id=...) AS 'weekly',
...
如果需要平均值,则可以使用子查询:
SELECT
monthly,
weekly,
monthly / total,
weekly / total
FROM (
SELECT
(SELECT COUNT(*) FROM items WHERE created_at>=... AND user_id=...) AS 'monthly',
(SELECT COUNT(*) FROM items WHERE created_at>=... AND user_id=...) AS 'weekly',
...,
(SELECT COUNT(*) FROM items WHERE user_id=...) AS total
) s
INDEX(user_id, created_at)
-最佳 AND created_at >= '2015-06-30 07:57:56'
帮助,因为它减少了要触摸的索引条目的数量 UNION
并没有帮助,因为它导致4倍的工作量。 SELECTs
并没有帮助。 也
COUNT(IF(created_at >= '2015-07-29 17:03:44', 1, null))
可以缩短为
SUM(created_at >= '2015-07-29 17:03:44')
(但可能不会加快很多速度)
如果数据不会随时间变化,则仅添加新行,然后,过去数据的摘要表将大大提高速度,但是前提是您必须避免在“ 30day”中使用“ 07:57:56”之类的方法。 (为什么只对其中一些使用“ 00:00:00”?)也许在其他更改的基础上,提速将是另外10倍。 想进一步讨论吗?
(我看不到使用PARTITION
任何优势。)
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