hi ,can you put a cockatiel and parakeet in the same cage?

i was thinking of buying a paraket this week somtime.when i have a day off.can you have both birds in the same cage together.a friend said you could but mentioned the different types of seeds they eat.
cockatiel's eat cockatiel seeds and parakeets eats parakeet seeds.
i could put one food dish with the seed that the cockatiel will eat on one side and he paraket seeds near the parakeet.

my cockatiel likes her cage door open so she can walk in & out of and stand on the door of it.but if i get a parakeet.i may not be able to leave the door open.


any idea's please i really want a parakeet for my son.he loves birds.
1st to give detailed good answer gets 10 points.thanks