paip.索引優化---sql distict—order by 法

paip.索引優化---sql distict—order by 法 

作者Attilax  

原語句:

select  SQL_NO_CACHE DISTINCT

    ( gaopinzi.HEZI),

     LEFT (hezi, 1) AS lft,

     RIGHT (hezi, 1) AS rit

    FROM

     gaopinzi 

    WHERE

     LENGTH(hezi) = 6    

        limit 50000

要7s中...網上說改用松散索引(複合索引) 會sbid fest...試了挂,  gaopinzi  force index(`all`)  ,基本沒效果..

函數索引應該好用着了,走十MYSQL不跟ORACLE牙十,不自此..

林吧,改為ORDER BY 形式..ONLY 0.3S

select  SQL_NO_CACHE

    max( gaopinzi.HEZI),

     LENGTH(hezi) = 6

      group by HEZI