paip.索引优化---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...网上说改用松散索引(复合索引) 会sbid fest...试了挂,  gaopinzi  force index(`all`)  ,基本没效果..
函数索引应该好用着了,走十MYSQL不跟ORACLE牙十,不自此..
林吧,改为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