Table structure for voting app
Here's how I would model the tables for that requirement (note the table and column names can be changed for whatever is appropriate for your application):



In this model, the idea of a "Profile" and "User" is contained in the same entity, "User". The idea of a single vote for one of two user candidates is contained in the entity "Vote". If you want to restrict a User to one Vote per set of two users, then you can add a unique index in Vote for idUser, idUserCandidate1, and idUserCandidate2.