Question

I have a litte problem here. I want to join twice from the same table, and group by a common value.
Here is the dataset (from table Voucher):

Date (dd/mm/yyyy)   Amount
--------------------------
01.01.2010          1.000
15.01.2010          2.000
01.03.2010          3.000
01.03.2010          4.000
01.05.2010          5.000
01.01.2011          1.000
01.02.2011          2.000
01.04.2011          3.000
15.04.2011          4.000
01.05.2011          5.000

The result should be like this:

Month   Amount 2010   Amount 2011
---------------------------------
1       3.000         1.000
2                     2.000
3       7.000
4                     7.000
5       5.000         5.000

How do I solve this?

Answer 1

Something along these lines will work for this case:

SELECT
    DATEPART(month,[Date]) as Month,
    SUM(CASE WHEN DATEPART(year,[Date]) = 2010 THEN Amount END) as [Amount 2010],
    SUM(CASE WHEN DATEPART(year,[Date]) = 2011 THEN Amount END) as [Amount 2011]
FROM
    Voucher
GROUP BY
    DATEPART(month,[Date]) as Month

For other situations, you might want to look into PIVOT.

Date is a really poor name for a column.