I have one table that I have turned into 2 tables. I have assigned aliases to the tables. So I have t1 and t2. There is one field in the tables that I have combined in a case statement to make a comparison. The query executes successfully, but rows are dropped periodically. How can I list both column names in the group by? I believe that this is the reason why I am dropping rows. The column name is time. So it would be t1.time and t2.time.