A mechanism is provided for secure data access in a data processing system. A database having two tables is provided. A subset of the tables' primary key attributes is considered sensitive. A first user is authorized to access the primary key's sensitive attribute in an unmasked format, while a second user is authorized to access same data in a masked format. Two security views are generated granting the second user access to the primary key's sensitive attribute values of both tables in the masked format. The masked format value is generated from an unmasked format value using a reversible function. A join operation between the two security views is performed by optimizing a query statement corresponding to the join operation.