Group BY

If Group By gives you an error the e.g (I got an error - Column 'Employee.EmpID' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause) Answer: Chances are that all the values in the column selected are unique and there is nothing to group by with/on. Group By works when there is data that resembles each other, then Group by will go and group those data value.