Including a SUM within a grouped UNION query

Question

Hi - I have inherited a (SSRS) report comprising two queries with a UNION. There is a requirement to add one extra column which SUMS a total for each resource per month. 
Grouping additional columns results in the following error:
Column 'dbo.MSP_EpmResource_UserView.ResourceName' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
Any help appreciated.

Answer 1

Your issue is that the subselect in your from block now contains a SUM but the other columns are not part of aggregate functions etc.
Even something simple like the following will give the same error:
CREATE TABLE #ForumExample (ColumnOne VARCHAR(3),ColumnTwo VARCHAR(3), ColumnThree VARCHAR(3), ColumnToBeSummed INT)
INSERT INTO #ForumExample
VALUES ('A','C','E',1),('A','C','E',2),('B','D','F',3),('B','D','F',4)
SELECT
 ColumnOne,
 SUM(ColumnToBeSummed)
FROM #ForumExample FE
DROP TABLE #ForumExample
To solve this, don't SUM the value in the subselect, just get each value for each row and then in the main SELECT block SUM the column and make sure to group by the summed result (not the column itself).
I havent had time to test this so I apologise if this doesn't work.