测试表：student
select * from studnet;
select count(distinct name) from student;
select count(distinct *) from student;
这样是有错误的，可以变通的实现
select count(*) from (select distinct * from student) st;
此路不通，我走另一条路！
SQL Server select count(distinct *)
原文：http://www.cnblogs.com/cnmarkao/p/4157961.html
