join with more keys and many files

I am looking for an easy way to join more than 2 datasets with several keys: my datasets have the colums: x, y, Par.

The datasets should be joined by the keys x and y

So the final dataset should have the columns: x y Par1 Par2 Par3...

Can I avoid to create an additional column xy where I combine x and y? Can I join more than two files in one step or at least avoid a for- or while-loop?