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  • paip.sql索引优化----join 代替子查询法

    paip.sql索引优化----join 代替子查询法

    作者Attilax ,  EMAIL:1466519819@qq.com
    来源:attilax的专栏
    地址:http://blog.csdn.net/attilax

     select SQL_NO_CACHE  *,(
        SELECT
         LEFT (fecye, 1)
        FROM
         cyefenbyao   force index(i_hezi) 
        WHERE
         cyefenbyao.hezi = rit
      limit 1
       ) AS rit_cye
      FROM
       (
        select  
        max( gaopinzi.HEZI) hezi,
         LEFT (hezi, 1) AS lft,
         RIGHT (hezi, 1) AS rit
        FROM
         gaopinzi 
        WHERE
         LENGTH(hezi) = 6
     
          group by HEZI

            limit 30000
       ) AS t2 


    要1S,改成join  0.5S..


    select SQL_NO_CACHE 
    t2.*  ,LEFT (fecye, 1) as t1
    FROM
     (
      SELECT
       max(gaopinzi.HEZI) hezi,
       LEFT (hezi, 1) AS lft,
       RIGHT (hezi, 1) AS rit
      FROM
       gaopinzi
      WHERE
       LENGTH(hezi) = 6
      GROUP BY
       HEZI
      LIMIT 30000
     ) AS t2

    left join  cyefenbyao
    on cyefenbyao.hezi = t2.rit


     


     

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  • 原文地址:https://www.cnblogs.com/keanuyaoo/p/3279838.html
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