SQL Server Query - groupwise multiplication

Question

If we have a table like this:

Grp       Value

Grp1          2
Grp1          5
Grp1          3
Grp2          3
Grp2         -5
Grp2         -2
Grp3                   


        

Answer 1

This comes from CodePlex "Aggregate Product function extends SQL". I modified the statement to return the desired results except for the NULL group, it returns "1".

    SELECT GrpID, Exp(Sum(IIf(Abs(ISNULL(value,1))=0,0,Log(Abs(ISNULL(value,1))))))*IIf(Min(Abs(ISNULL(value,1)))=0,0,1)*
(1-2*(Sum(IIf(ISNULL(value,1)>=0,0,1)) % 2)) AS value 
    FROM @foo
    GROUP BY GrpID;

GrpID     Value

Grp1       30
Grp2       30
Grp3        0
Grp4        8
Grp5        7
Grp6        1
Grp7      -10

ref: http://productfunctionsql.codeplex.com/