paip.索引优化---sql distict―order by法_MySQL

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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

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