Originally Posted by zergi
Often in real world apps it is more comfortable to work with a single column id, rather that with multi-column key
Absolutely agree! But that is only true if you will *USE* that single column id.
In this case, where the table you (correctly!) proposed is a many-to-many table, I can't see any case where you would need to *REFER* to records therein. (If you can make such a case, I'll reverse my position, of course.)
Mind you, it is *NOT* a major point, and that's why I said I disagreed in only a minor way. It's not going to hurt to have an added auto_increment ID there; I just don't see it as adding any value.
Glad to see another DB fan join in here. Welcome!