我的查询最多需要 40 秒才能执行,我想知道如何让它更快......
SELECT rp.`id` as rip,r.`id`,
rl.`id` as rlid, r.`number`, r.`type`,
a.`title` as atitle, a.`id` as aid, more,
more_valid
FROM
`R_l_p` rp INNER JOIN
`Rl` rl ON rp.`rl_id` = rl.`id` INNER JOIN
`R` r ON r.`id` = rl.`r_id` INNER JOIN
`A` a ON a.`id` = r.`a_id`
LEFT JOIN
(SELECT `type`, `v`, `r_id`, COUNT(*) AS more
FROM `R_l`
WHERE `type` = 'stream' AND `v` = 1
GROUP BY `r_id`) stm ON stm.`r_id` = r.`id`
LEFT JOIN
(SELECT `type`, `v`, `r_id`, COUNT(*) AS more_valid
FROM `R_l`
WHERE `type` = 'stream' AND `v` = 0
GROUP BY `r_id`) morelink ON morelink.`r_id` = r.`id`
WHERE rp.`link` = 'dead' AND rl.`type` = 'stream'
ORDER BY rip ASC
LIMIT 0, 1000
+-----+--------------+---------------+---------+--------------------------+-------------+----------+---------------------------+--------+----------------------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +-----+--------------+---------------+---------+--------------------------+-------------+----------+---------------------------+--------+----------------------------------------------+ | 1 | PRIMARY | r | ALL | PRIMARY,a_id | NULL | NULL | NULL | 21804 | Using temporary; Using filesort | | 1 | PRIMARY | a | eq_ref | PRIMARY | PRIMARY | 4 | db453988339.r.a_id | 1 | | | 1 | PRIMARY | rl | ref | PRIMARY,r_id,type | r_id | 4 | db453988339.r.id | 1 | Using where | | 1 | PRIMARY | derived2 | ALL | NULL | NULL | NULL | NULL | 21077 | | | 1 | PRIMARY | derived3 | ALL | NULL | NULL | NULL | NULL | 1 | | | 1 | PRIMARY | rp | eq_ref | rl_id | rl_id | 4 | db453988339.rl.id | 1 | Using where | | 3 | DERIVED | R_link | ALL | type | NULL | NULL | NULL | 27580 | Using where; Using temporary; Using filesort | | 2 | DERIVED | R_link | ALL | type | NULL | NULL | NULL | 27580 | Using where; Using temporary; Using filesort | +-----+--------------+---------------+---------+--------------------------+-------------+----------+---------------------------+--------+----------------------------------------------+
谢谢你:)
最佳答案
一方面,我将用一个内联 View 替换两个内联 View ,通过将条件从WHERE 子句插入 SELECT 列表中的表达式),并消除 more_link
View 。
我会将 stm
内联 View 修改为如下所示:
( SELECT q.r_id
, SUM(q.v=1) AS `more`
, SUM(q.v=0) AS `more_valid`
FROM `R_l` q
WHERE q.type = 'stream'
GROUP BY q.r_id
) stm
我还会提供一个覆盖索引来优化该内联 View 查询,例如:
CREATE INDEX R_1_IX1 ON R_1 (type, r_id, v)
在前导列 type
上使用相等谓词,MySQL 可以使用索引优化 GROUP BY 操作(避免“使用文件排序”操作)。我们希望在解释的额外列中看到“使用索引”。
不幸的是,派生表不会被索引。但至少通过这一更改,您只具体化了一个内联 View ,避免了额外的连接操作。
也就是说,我将替换这两行:
LEFT JOIN (SELECT `type`, `v`, `r_id`, COUNT(*) AS more FROM `R_l` WHERE `type` = 'stream' AND `v` = 1 GROUP BY `r_id`) stm ON stm.`r_id` = r.`id`
LEFT JOIN (SELECT `type`, `v`, `r_id`, COUNT(*) AS more_valid FROM `R_l` WHERE `type` = 'stream' AND `v` = 0 GROUP BY `r_id`) morelink ON morelink.`r_id` = r.`id`
有了这个:
LEFT
JOIN ( SELECT q.r_id
, SUM(q.v=1) AS `more`
, SUM(q.v=0) AS `more_valid`
FROM `R_l` q
WHERE q.type = 'stream'
GROUP BY q.r_id
) stm
ON stm.r_id = r.id
关于mysql - 优化sql查询,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25983653/