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

+-----+--------------+---------------+---------+-- ------------+-------------+----------+ ---------------+--------+------------- ---------------------------------+ |编号 |选择类型 |表|类型 |可能的键 |关键 | key_len |参考 |行 |额外 | +-----+--------------+---------------+---------+-- ------------+-------------+----------+ ---------------+--------+------------- ---------------------------------+ | 1 |初级 | r |全部 |初级，a_id |空 |空 |空 | 21804 |使用临时的；使用文件排序 | | 1 |初级 |一个 | eq_ref |初级 |初级 | 4 | db453988339.r.a_id | 1 | | | 1 |初级 | rl |参考 | PRIMARY,r_id,类型 | r_id | 4 | db453988339.r.id | 1 |使用位置 | | 1 |初级 |派生2 |全部 |空 |空 |空 |空 | 21077 | | | 1 |初级 |派生3 |全部 |空 |空 |空 |空 | 1 | | | 1 |初级 | rp | eq_ref | rl_id | rl_id | 4 | db453988339.rl.id | 1 |使用位置 | | 3 |派生 |链接 |全部 |类型 |空 |空 |空 | 27580 |使用哪里；使用临时的；使用文件排序 | | 2 |派生 |链接 |全部 |类型 |空 |空 |空 | 27580 |使用哪里；使用临时的；使用文件排序 | +-----+--------------+---------------+---------+-- ------------+-------------+----------+ ---------------+--------+------------- ---------------------------------+

谢谢你:)

Answer 1

一方面，我会用一个内联视图替换两个内联视图，通过将 WHERE 子句中的条件移动到 SELECT 列表中的表达式中，从同一个内联视图返回 more 和 more_valid），并消除more_link 视图。

我会将stm 内联视图修改为如下所示：

       ( 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视图查询，例如：

    CREATE INDEX R_1_IX1 ON R_1 (type, r_id, v)

使用前导列type 上的相等谓词，MySQL 可能能够使用索引优化 GROUP BY 操作（避免“使用文件排序”操作）。我们希望在说明的额外列中看到“使用索引”。

很遗憾，派生表不会被索引。但至少通过这种更改，您只实现了一个内联视图，避免了额外的连接操作。

---

也就是说，我会替换这两行：

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