sql - 使用无限数量的不同值进行透视

Question

我写了这个查询:

SELECT s, [1] AS a1, [2] AS a2, [3] AS a3, [4] AS a4
FROM (SELECT grade, aid, s FROM m) p
PIVOT
(
SUM(grade)
FOR aid IN ([1], [2], [3], [4])
) AS pvt ORDER BY pvt.s;

返回结果:

s  a1  a2  a3  a4
1  25  69  95  56
2  27  99  16  87
. . . .
99 98  12  34  76

这正是我想要的结果。我的问题是“援助”并不总是有四个不同的值(value)观。是否可以重写此查询(或使用存储过程)，以便“a*”列的数量取决于“aid”中有多少个不同值？

Answer 1

您将需要使用动态数据透视来获取所需的列列表。这将首先检索列的列表，然后旋转该列表。与此类似的东西:

DECLARE @cols AS NVARCHAR(MAX),
    @query  AS NVARCHAR(MAX);

select @cols = STUFF((SELECT distinct ',' + QUOTENAME(aid) 
            FROM m 
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT s, ' + @cols + ' from 
            (
                select grade, aid, s
                from m
           ) x
            pivot 
            (
                sum(grade)
                for aid in (' + @cols + ')
            ) p 
            ORDER BY p.s'

execute(@query)