where Cname like ‘DB\Design‘ escape‘\‘; --escape‘\‘ 表示‘\‘--
聚集函数
select count(distinct sno)
select avg(grade)
select max(grade)
select sum(ccredit)
聚集函数只能用于select字句和group by 中的having字句
select sno
from sc
group by sno
having count(*)>3
having短句用于组，从中选择满足条件的组
原文：http://www.cnblogs.com/Arvin-9/p/5124310.html