Oracle and Postgresql

Hello,

I am a CS graduate and I have a brief idea of Postgres and Oracle.
But, I dont have an in-depth knowledge in any of them. I have a couple
of questions and

I want to compare both of them in terms of functionality, performance,
advantages and disadvantages.

Why most enterprises prefer Oracle than Postgres even though it is
free and has a decent enough user community.

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Thanks,
Srinivas