mysql的ORDER BY RAND()优化_MySQL

[php] $DBI=new dbi2($__DBserver);  $num=$DBI->result('select count(1) as num from article');//获取总条数，数据库引擎为MyISAM采用吧  $num=$num[0]['num']-1;  $num=rand(1, $num);  $list=$DBI->result('SELECT id FROM acticle ORDER BY viewcount DESC LIMIT ?,1',$num);//利用limit  

[php] $DBI=new dbi2($__DBserver);  //在200条范围内取10条随机  $list=$DBI->result('SELECT id FROM (SELECT id FROM acticle ORDER BY viewcount DESC LIMIT ?)X ORDER BY RAND() LIMIT ?',200,10);