SQL 2016's RLS Feature allows you to implement restrictions on data row access. You can use this business rule manager to enforce rules that are difficult to achieve through the data layers or the API wrappers that talk to database and extract code.
You can thus enforce business rules such as, when Client A runs a SELECT Query, the database will never return data of any other client.
It is a three step process: Set the session context on a SQL connection, create Security Policy and Predicate function and you are all set.
Refer to Microsoft's documentation on this useful feature here.