The LAMP-stack community frequently shows their disdain for foreign and primary keys in databases, and sometimes with reason borne of experience. MySQL historically has been little more than a nice language for comparing a set of unrelated spreadsheets, so referential integrity has had to happen at the application layer or not at all. As such, careful MySQL users put a lot of work into ensuring referential integrity, without the help of the database.
But the eyes of even the most hardened LAMPer would widen, if he were to dip into a conversation to find someone saying the following about something they’ve built over PostgreSQL:
Yeah, I could add the current date/time to the end, so as long as you don’t add more than one [entry] with the same name within 1 second, it’ll be fine.
It might take you a while to work out (a) what that’s referring to (b) what kind of error in thinking it demonstrates and (c) what it implies about the quality of the underlying code. By that time—if you’ve worked at all with that sort of programming—your head may well be in your hands.