Recommending movies customers haven't rented yet based on their favorite genres, according to their rental history
Most common ...

In statistics, this is called mode.

Yes, PostgreSQL has an aggregate called mode.  I haven't messed with it in PostgreSQL.

Retrieves those not wanted...

You want the resulting set of all movies for a genre minus the data set containing all movies rented by a customer for that genre

In PostgreSQL, you'll want to say EXCEPT instead of MINUS.