paip.索引優化---sql distict—order by法

paip.索引優化---sql distict—order by法  

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(復合索引) 會sbid fest...試了掛,  gaopinzi  force index(`all`)  ,基本沒效果.. 函數索引應該好用著了,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),
     LEFT (hezi, 1) AS lft,
     RIGHT (hezi, 1) AS rit
    FROM
     gaopinzi  
    WHERE 
     LENGTH(hezi) = 6

      group by HEZI

        limit 50000

 

  我的MYSQL VER是.5.0.45-community-nt