独立子查询：
select * from TblStudent where tSClassId = (select tClassId from TblClass where tClassName = '高二二班')
独立子查询：
select * from TblStudent as ts where exists(select * from TblClass as tc where ts.tSClassId=tc.tClassId and tc.tClassName = '高二二班')
所有查询都可以用相关子查询来代替
where 列名 = 一个值
where 列名 in 几个值
---------------------分页-------------
--要求，每页显示10条 首先要确定排序
--第一页
select top (10*2) * from Customers order by CustomerID asc
--要查询第2页思路：先查询前2-1的customerId
select top 10 * from Customers where CustomerID not in (
select top (10 * (2-1)) CustomerID from Customers order by CustomerID asc)
order by CustomerID asc
--查询最后一页数据，每页5条数据
select top 5 * from Customers where CustomerID not in (
select top (5 * (((select count(*) from Customers)/5))) CustomerID from Customers order by CustomerID asc)
order by CustomerID asc
select * from Customers order by CustomerID asc
--查询最后一页数据，每页5条数据
select* from Customers where CustomerID in(
select top 10 CustomerID from Customers order by CustomerID desc) order by CustomerID asc
--查询第一页数据，每页5条数据
select top 10 * from Customers order by CustomerID asc
---分页另一种思路：使用Row_Number()函数------
--使用row_nuber()实现
--1、添加一列，专门为数据排序，然后编号
select * ,RN = ROW_NUMBER() over (order by CustomerID)from Customers
--2、根据用户要查看的每页记录数，以及要查看第几页，确定应该查询第几条到第几条
--查询第五页，每页8条
select * from (select * ,RN = ROW_NUMBER() over (order by CustomerID)from Customers ) as t where t.RN between (5-1)*8+1 and 5*8
