Twins are two extensions onto SQL to support user privacy in social networks: one is corporate-based and the other is user-centric, corresponding to well-known mandatory access control and discretionary access control models, respectively. This paper illustrates the former. The approach adds some predicates to the CREATE TABLE command to capture common corporate-based user privacy requirements, such as purpose, generalization, and retention, required by social networks desiring to support privacy. Hence, the corporation, when creating the underlying databases, defines what the mandatory privacy policies are with which all users must comply. The extension is supported with underlying catalogues, algorithms, and prototype. The key contribution is a low-cost mechanism to develop new systems-that are privacy-preserved-and to transform legacy database MAC models to their privacy preserving equivalents. Although our examples are from social networks, the results apply to data security and user privacy of other enterprises too.