我有两张桌子:
CREATE TABLE `album` (
`album_id` int(10) unsigned NOT NULL,
`artist_id` int(10) unsigned NOT NULL,
`album_type_id` int(10) unsigned NOT NULL,
`name` varchar(255) NOT NULL,
`first_released` year(4) NOT NULL,
`country_id` smallint(5) unsigned DEFAULT NULL,
PRIMARY KEY (`album_id`),
KEY `artist_id` (`artist_id`),
KEY `name` (`name`)
) ENGINE=InnoDB
CREATE TABLE `artist` (
`artist_id` int(10) unsigned NOT NULL,
`type` enum('Band','Person','Unknown','Combination') NOT NULL,
`name` varchar(255) NOT NULL,
`gender` enum('Male','Female') DEFAULT NULL,
`founded` year(4) DEFAULT NULL,
`country_id` smallint(5) unsigned DEFAULT NULL,
PRIMARY KEY (`artist_id`),
KEY `name` (`name`)
) ENGINE=InnoDB;
我的第一个问题:
select ar.name, count(*)
from artist ar
join album al on ar.artist_id=al.artist_id
group by ar.artist_id
limit 10;
产生0.00秒的结果集.
我想订购结果,所以我添加“order by 2 desc”:
select ar.name, count(*)
from artist ar
join album al on ar.artist_id=al.artist_id
group by ar.artist_id
order by 2 desc
limit 10;
但现在结果集超过5秒,这太慢了.
执行计划:
如何添加索引以加快我的新查询?
最佳答案 首先,您应该使用索引列进行选择和计数,这将按性能进行更好的排序,然后您可以在筛选结果上加入艺术家名称以完成数据.有点像.
SELECT ar2.name, t.c
FROM
(
SELECT ar.artist_id, COUNT(*) c
FROM artist ar
JOIN album al ON ar.artist_id=al.artist_id
GROUP BY ar.artist_id
ORDER BY 2 DESC
LIMIT 10
)
t JOIN artist ar2 ON ar2.artist_id=t.artist_id
我尝试使用您的数据,只需不到1秒.希望这有帮助