As a senior DBA that has done many interviews for more junior DBA/database developer, I too have been surprised by how many candidates cannot answer a question like that at all.

With that said, many developers (other than database developers) really do not need to understand that. They don't need to understand it because they will normally have a good DBA/database developer that handles that part for them. In fact, large projects may have many specialized DBA roles including Architects focused specifically on schema design.