SELECT COUNT(DISTINCT companyId) FROM w_his_recommend h LEFT JOIN w_admin a ON h.adminId = a.id WHERE a.adminName='lisi' 以上SQL优化,据说distinct很是影响速度,如何将上述的distinct去掉还可以得到相同的结果,求帮助,线等!
SELECT COUNT(companyId)
FROM w_his_recommend h
LEFT JOIN w_admin a ON h.adminId = a.id
WHERE a.adminName='lisi'
group by companyId
看看执行计划呢?companyId建索引