MySql count 去掉反复 Home » IDC云服务 » MySql count 去掉反复 MySql count 去掉重复 1. select count(distinct CName) from Course 2. select count(CName) from (select distinct CName from Course) as temp as可有可无。temp作为别名,若无则提示错误:1248 – Every derived table must have its own alias