What is the difference between MIDI controller and a DJ Mixer?

Question by Nancy: What is the difference between MIDI controller and a DJ Mixer?
I am trying to learn about this stuff so I can become a dj. I just bought 2 pioneer cdj -200 and a stanton sx202 mixer. I have been looking online and it seems like everyone uses virtual DJ, traktor pro etc and midi controller.
So what exactly does a DJ mixer do and what does MIDI controller do?
what is the basic DJ set up? cd player>mixer>computer(with virtual dj, traktor etc),>MIDI contoller>active pa

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