I'm assuming that this related to GDPR; which is coming into effect in 2018.

In all honesty, I don't really know at this time. We have a Data Protection Officer (DPO) here who's keeping up to speed, but here in the UK the legislation isn't finalised yet (and it's the same to a degree in the EU); mainly due to "BREXIT"... /sigh (can you tell I'm pro EU? 😉 ). This means that you know you need to segregate the data, but not really told how to (the business needs to decide until real guidelines are put in place, if at all).

From my understanding from the DPO (who's sitting behind be), the important part is the proof that your data is segregated, and thus, the how doesn't matter provided that the method you've chosen is effective and you can prove as such. For example, if you simply choose to use Row Level Security/Partitioned view to enforce access for specific users, that is still a form is segregation. Alternatively, you could go as far as storing the data in a different table, different database, or even a totally different instance/Server and/or (physical) location.

The best person to speak to will be your DPO at your company. They should be the most informed on what the current regulations and laws are that affect your clients, and can give you pointers on what they see your business requirements are. Every company is unique, with different systems and processes in place, so there's going to be no "blanket" answer to a question like this, just recommendations; and normally the right person in the business will be the best person to give those for others to then implement. 🙂