Patrick’s Unique Identifier Dictum (PUIDD): If you need to assign unique identifiers in order to differentiate two records in a database, you don’t need to differentiate those two records in that database.

(No, this is not always true. I think the ratio of how often it is true to how often informatics people believe it is true, though, is very high. It’s at least worth asking what a UID is intended to accomplish in any particular case, rather than assuming that they are universally desirable.)