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mysql随机读取记录order by rand()优化

‘SELECT id,cover,intro,tel,title,areaid,posttime,bigsortid,sortid FROM cinfos WHERE id>=(SELECT floor(RAND()*((SELECT MAX(id) FROM cinfos)-(SELECT MIN(id) FROM cinfos))+(SELECT MIN(id) FROM cinfos))) and isshow=1 ORDER BY id LIMIT 2’