What happens if I buy a game without the DLC's the first time and then want to buy the game with all the DLC's

I first bought the normal version of Civ V without all the DLC's, but that was really boring, so I wanted the complete edition. That was $40, so I waited until the sale.

I want to buy the complete edition, now. Will I get 2 copies, just all the DLC's, or nothing at all?

I've been in the same situation with Civ 5 and also Killing Floor.

If you own the base game, but not the DLC, buying a complete/gold edition will give you all the DLC but not another copy of the base game.

In some cases it's cheaper than buying all the DLC on its own, even though you're missing out on the base game (Civ 5/Killing Floor case).