Can I connect a "constant" power source to a "switch controlled" power source in the same junction box?

I am putting power to the deck at the rear of my house. One line ( "switch controlled " ) is for the lights, and the " constant power ", is for a GFI, as I don't want to have the GFI tied into the lights so that in order for the GFI outlet to work, the lights have to be on.

I am wondering if I run both sets of wires through the same junction box will it cause a problem?

Please explain further.

You can have switchlegs, hots, GFI in same box, and conduit, you do have to watch box fill, and wire fill. Neutral for the light would have to go to neutral before gfi. Other wise when you turn on light, the gfi will trip.