编写高级SQL选择

Question

物品表:

|   Item    |   Qnty    |   ProdSched   |
|    a      |    1      |       1       |
|    b      |    2      |       1       |
|    c      |    3      |       1       |
|    a      |    4      |       2       |
|    b      |    5      |       2       |
|    c      |    6      |       2       |

有没有办法可以使用SQL输出它SELECT？

|   Item    |   ProdSched(1)(Qnty)  |   ProdSched(2)(Qnty)  |
|    a      |           1           |       4               |
|    b      |           2           |       5               |
|    c      |           3           |       6               |

Answer 1

你可以用PIVOT它.如果要转换已知数量的值,则可以通过静态数据透视表对值进行硬编码:

select item, [1] as ProdSched_1, [2] as ProdSched_2
from 
(
  select item, qty, prodsched
  from yourtable
) x
pivot
(
  max(qty)
  for prodsched in ([1], [2])
) p

看看SQL Fiddle with Demo

如果列数未知,则可以使用动态数据透视表:

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

select @cols = STUFF((SELECT distinct ',' + QUOTENAME(prodsched) 
                    from yourtable
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,1,'')

set @query = 'SELECT item,' + @cols + ' from 
             (
              select item, qty, prodsched
              from yourtable
            ) x
            pivot 
            (
                max(qty)
                for prodsched in (' + @cols + ')
            ) p '

execute(@query)

看看SQL Fiddle with Demo