Hi Vamsi -
By definition, when one uses the JOIN clause, you must specify two or more related columns - unless you want to create a cartesian product via a CROSS JOIN. For more information, try reading the following: Join (SQL) - Wikipedia, the free encyclopedia
How would merging these two sheets actually help you? I took a quick look at them, and I don't see why merging them would do much for you.
In any case, you're trying to "fight" the behavior of how SQL JOINs work. Tableau can't help you much there.