Question

I’m using SQL Server 2008 R2 and I have a database which contains two tables.

T1 contains raw data, however only the column Cost, Date and AccId is interesting for me.

T2 contains a few columns like Jan, Feb, Mar, Apr, … and a column AccId

I need now a stored procedure which sets the values in the appropriate column in T2 whenever I update T1. It should sum up the Cost for every AccId in the given month. If I set @year = 2012 and @month = 3, so it should update the column Mar with the sum of Cost in T2 for every AccId, which is in T1 and T2.

I have now a stored procedure which would work for one constant column. I want now CASE which selects the column depending on the given month. Here is a stored procedure how I think it should work, but it doesn’t work:

CREATE PROCEDURE [dbo].[SP_Calc]
    @year int,
    @month int
AS

    MERGE INTO T2
    USING (
            SELECT AccId, SUM(Cost) AS CostSum
            FROM T1
            WHERE YEAR(Date) = @year
            AND MONTH(Date) = @month
            GROUP BY AccId
         ) AS source
      ON T2.AccID = source.AccId
    WHEN MATCHED THEN
    UPDATE SET 
     SELECT 
       CASE @month 
        WHEN 1 THEN Jan = source.Cost
        WHEN 2 THEN Feb = source.Cost
        WHEN 3 THEN Mar = source.Cost
        WHEN 4 THEN Apr = source.Cost
        WHEN 5 THEN Mai = source.Cost
        WHEN 6 THEN Jun = source.Cost
        WHEN 7 THEN Jul = source.Cost
        WHEN 8 THEN Aug = source.Cost
        WHEN 9 THEN Sep = source.Cost
        WHEN 10 THEN Oct = source.Cost
        WHEN 11 THEN Nov = source.Cost
        WHEN 12 THEN Dez = source.Cost
        ELSE RAISERROR ('Month is out of range', 18, 1); 
    END

Answer 1

You don’t have a Cost in your Source, just CostSum

Also you need to change your setting to

SET
   Jan = CASE @month  WHEN 1 THEN source.CostSum else T2.Jan end,
   Feb = CASE @month  WHEN 2 THEN source.CostSum else T2.Feb end,
...