I always use normalization/database design as an interview question. I firmly believe that good questions about database design can really identify the candidate's skills and weaknesses in this area:

- it works well sitting around a whiteboard, which is a nice friendly dynamic that emulates how we really work

- it doesn't require detailed/arcane recollection of specifics, is more conceptual. Who wants to fail someone because they don't remember a parameter or some specific details of how TreeMaps work?

- it can't be faked - no-one can talk their way through a database design discussion unless they really have an aptitude for it

- its interesting. Who doesn't want to spitball around, say, modelling what Uber's database might look like behind the scenes.

I would say there are plenty of decent programmers around who can't (or haven't) done any real database design work, but if its a core skill (SaaS app development) that you really need, then its an easy one to detect at interview.

No. Source: I have worked for a financially successful company whose database was designed without any notion of foreign keys or surrogate keys. They also had serialized Java objects in database blobs by accident.

I've worked for several like that. The blob antipattern isn't uncommon.