mysql - 优化sql查询

Question

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:)

Answer 1

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