MySql count去掉重复语句_MySQL

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MySql count去掉重复语句 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 
  摘自 王贺的博客 bitsCN.com