-- 开窗函数：在结果集的基础上进一步处理(聚合操作)

-- Over函数,添加一个字段显示最大年龄
SELECT  * ,
        MAX(StuAge) OVER ( ) MaxStuAge
FROM    dbo.Student;

-- Over函数,添加一个字段显示总人数
SELECT  * ,
        COUNT(StuID) OVER ( ) StuCount
FROM    dbo.Student;

-- Partition By 分组统计数量
-- 根据性别分组后，统计 
SELECT  COUNT(*) OVER ( PARTITION   BY StuSex ) ,
        *
FROM    dbo.Student; 

-- 根据班级分组后，统计、排序 
SELECT  COUNT(*) OVER ( PARTITION   BY Class ORDER BY Height) ,
        *
FROM    dbo.Student; 

-- Over函数,添加一个字段显示平均身高
SELECT  * ,
        AVG(Height) OVER ( ) AgeHeight
FROM    dbo.Student;

--Row_Rumber()
SELECT  ROW_NUMBER() OVER ( ORDER BY StuID DESC ) RowNumber ,
        *
FROM    dbo.Student 

--Row_Rumber() 实现分页效果
;
WITH    T AS ( SELECT   ROW_NUMBER() OVER ( ORDER BY StuID DESC ) RowNumber ,
                        *
               FROM     dbo.Student
             )
    SELECT  *
    FROM    T
    WHERE   T.RowNumber BETWEEN 1 AND 3;

--Rank() 排名函数,名次相同，跳过
SELECT  RANK() OVER ( ORDER BY Height ) ,
        *
FROM    dbo.Student;

--DENSE_Rank() 排名函数，名次相同不跳过
SELECT  DENSE_RANK() OVER ( ORDER BY Height ) ,
        *
FROM    dbo.Student;

-- NTILE()函数，参数：记录总数/划分区域 = 每个区域数组，把记录序号放进数组 (平均分组)
SELECT  NTILE(3) OVER ( ORDER BY StuSex ) ,
        *
FROM    dbo.Student;