Comparing three column records in a mysql table

I make a query in COL1 which has the total of rows and then I make a query in COL2, but it is less than COL1. How do I get COL2 to return the IDs that are the same as COL1 so that they are side by side according to the ID of COL1 so I can see who is the same and who is different. Do I have to zero in on COL2 by pushing the IDs down to match the IDs?