Virtual Private Database (VPD), also referred to as row-level security or RLS, is a feature built into the Oracle Database that allows you to set up security policies on tables that restrict which rows a user can see or change based on the policy logic. One of the nicest things about VPD is that this logic (and the fact that a filter is being applied) is completely invisible to the user. They just see the data relevant to them and none the wiser about all that other data in the data. Here's a simple example to drive the point home: suppose I am building a health care application and it contains a patients table. The security policy is straightforward: A patient can only see their own information. A doctor can see only the information about their own patients. A clinic administrator can see information only about the patients in their clinic. In all three cases, the user would sign on to the application and execute this identical query and only their rows would appear.
For the last twenty years, I have managed to transform an obsession with PL/SQL into a paying job. How cool is that?