How to map a five comapny in one Database?

now i want to map a five comapny for separate Five users…i.e.A company Map to A user,B Company Is Map to B User…Like that I want To map all the user and company…but User A is should not get access to company B i.e.user A Should not see the company B data Respectively…

No such feature out of the box, use separate sites / databases.