MySQL性能差

Question

我有一个带有多个左连接的Distinct Select语句，当我的where子句很大时，该语句的性能很差。 以下是我的声明

SELECT  DISTINCT u.*, ri.id as reg_id, d.id as dist_id
    FROM  users u
    LEFT JOIN  earned_points ep ON u.id = ep.user_id
    LEFT JOIN  distributors d ON d.id = ep.distributor_id
      OR  d.id = u.distributor_id
      OR  d.id = u.additional_distributor_id
    LEFT JOIN  registration_items_users riu ON u.id = riu.user_id
      AND  riu.distributor_id = d.id
      AND  riu.registration_item_id = 21
    LEFT JOIN  registration_items ri ON riu.registration_item_id = ri.id
    WHERE  d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
               1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
               1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931 );

该查询的解释如下：

此查询大约需要4秒钟才能完成。 如果我将where减少到一个id，那么它最多可以加速170ms。

将不胜感激有关如何使此查询更快的任何建议。

谢谢

编辑

我能够根据Rick James（接受的答案）的建议提出一个解决方案。 使用Union并摆脱Left Joins and Distinct可以达到目的。 与上面的4秒版本相比，此新查询大约需要200毫秒。

(SELECT  u.*, 
   (SELECT riu.registration_item_id 
       FROM registration_items_users riu 
       WHERE riu.user_id = u.id 
           AND riu.distributor_id = d.id 
           AND riu.registration_item_id = 21) as reg_id,
   d.id as dist_id
   FROM users u
   JOIN earned_points ep ON u.id = ep.user_id
   JOIN distributors d ON d.id = ep.distributor_id
       WHERE d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
            1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
            1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931))
   UNION
(SELECT  u.*, 
   (SELECT riu.registration_item_id 
       FROM registration_items_users riu 
       WHERE riu.user_id = u.id 
           AND riu.distributor_id = d.id 
           AND riu.registration_item_id = 21) as reg_id,
   d.id as dist_id
   FROM users u
   JOIN distributors d ON d.id = u.distributor_id
       WHERE d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
            1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
            1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931))
   UNION
(SELECT  u.*, 
   (SELECT riu.registration_item_id 
       FROM registration_items_users riu 
       WHERE riu.user_id = u.id 
           AND riu.distributor_id = d.id 
           AND riu.registration_item_id = 21) as reg_id,
   d.id as dist_id
   FROM users u
   JOIN distributors d ON d.id = u.additional_distributor_id
       WHERE d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
            1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
            1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931))

Answer 1

在EXPLAIN ，查看u行。 它正在执行大约6974行的“表扫描”。

除非“ right”表是可选的，否则请摆脱LEFT 。

将OR变成UNION ; 那就是索引使您失败的地方。 （ UNION ALL比UNION DISTINCT快；请选择任何一个有意义的。）

假设可以删除LEFTs ，并且可以将DISTINCT从SELECT移到UNION ：

SELECT  u.*, ri.id as reg_id, d.id as dist_id
    FROM  users u
    JOIN  earned_points ep ON u.id = ep.user_id  -- ep needed only for this
    JOIN  distributors d ON d.id = ep.distributor_id  -- This one line differs
    JOIN  registration_items_users riu ON u.id = riu.user_id
      AND  riu.distributor_id = d.id
      AND  riu.registration_item_id = 21
    JOIN  registration_items ri ON riu.registration_item_id = ri.id
    WHERE  d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
                1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
                1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931 
                   )
    UNION  DISTINCT 
SELECT  u.*, ri.id as reg_id, d.id as dist_id
    FROM  users u
    JOIN  distributors d ON d.id = u.distributor_id
    JOIN  registration_items_users riu ON u.id = riu.user_id
      AND  riu.distributor_id = d.id
      AND  riu.registration_item_id = 21
    JOIN  registration_items ri ON riu.registration_item_id = ri.id
    WHERE  d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
                1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
                1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931 
                   )
    UNION  DISTINCT 
SELECT  u.*, ri.id as reg_id, d.id as dist_id
    FROM  users u
    JOIN  distributors d ON d.id = u.additional_distributor_id
    JOIN  registration_items_users riu ON u.id = riu.user_id
      AND  riu.distributor_id = d.id
      AND  riu.registration_item_id = 21
    JOIN  registration_items ri ON riu.registration_item_id = ri.id
    WHERE  d.id IN (201,281,321,631,901,971,1211,1601,1611,1621,
                1631,1641,1651,1661,1671,1681,1691,1701,1711,1721,1731,
                1741,1751,1761,1771,1781,2281,2291,2401,2781,2801,2931 
                   ) ;

跨列展开数组通常是一个坏主意。 这似乎是distributors正在发生的事情。 这种混乱可能是这种情况的结果。

编辑

更好的是将ri和rui内容从选择中拉出，并将其转换为子查询。 这是要点； 我没有精力写这一切：

SELECT x.*,
        ( SELECT ... ri and rui stuff ... ) AS reg_id
    FROM (
        --  from above, less the ri and rui stuff:
        SELECT ...
        UNION DISTINCT
        SELECT ...
        UNION DISTINCT
        SELECT ...
         ) AS x;