PostgreSQL Row Level Security: A Complete Guide

Your application code knows which tenant owns which row. Your ORM always filters by WHERE tenant_id = $1 . Your team has reviewed the queries and they look fine. Then someone forgets the WHERE clause. Or a bulk operation skips the filter. Or a new developer writes a raw query without knowing the convention. Suddenly one tenant can read another tenant's data, and you find out from a support ticket two weeks later. Row Level Security (RLS) moves the tenant isolation logic inside PostgreSQL itself.