So something nice about a real database is cascading values, most commonly used to deletion, but you can use them for updates as well. Let me give you a scenario: I track groups of data from my clients by a sub_id field. As they add groups, their ids aren’t in a range. If I wanted to consolidate them, I could update the sub_id (somewhere that won’t be stomped on by the sequence), but what about historical data.

Mas.

http://alexhochberger.com/2009/09/10/postgresql-cascading-updates-and-deletes/