Write advanced SQL Select

问题:

Item table:

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

Is there a way I can output it like this using SQL SELECT?

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

回答1:

SELECT Item, 
  [ProdSched(1)(Qnty)] = MAX(CASE WHEN ProdSched = 1 THEN Qnty END),
  [ProdSched(2)(Qnty)] = MAX(CASE WHEN ProdSched = 2 THEN Qnty END)
FROM dbo.tablename
GROUP BY Item
ORDER BY Item;

回答2:

You can use PIVOT for this. If you have a known number of values to transform, then you can hard-code the values via a static pivot:

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

see SQL Fiddle with Demo

If the number of columns is unknown, then you can use a dynamic pivot:

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)

see SQL Fiddle with Demo

回答3:

Let's hit this in two phases. First, although this is not the exact format you wanted, you can get the data you asked for as follows:

Select item, ProdSched, max(qty)
  from Item1
 group by item,ProdSched

Now, to get the data in the format you desired, one way of accomplishing it is a PIVOT table. You can cook up a pivot table in SQL Server as follows:

Select item, [1] as ProdSched1, [2] as ProdSched2
from ( Select Item, Qty, ProdSched
         from item1 ) x
Pivot ( Max(qty) for ProdSched in ([1],[2]))  y