Knowing to use indexes you should know, and I know it from practical experience, not from learning comp science or theory. However I don't know sorting algorith

Knowing to use indexes you should know, and I know it from practical experience, not from learning comp science or theory. However I don't know sorting algorithms top of my head and their complexities, since database does the sorting and heavy lifting underneath. This is the key difference. When I have gone through FAANG level companies, I spent 2 weeks preparing and learning the fundamental theory, a year or two later I have forgotten most of this and I'd have to prepare like that again. It's interesting and can be useful to go through the material on how database engine exactly works underneath, but you definitely shouldn't have to memorise this long after you went through the material and you probably won't use this information in your real life, except for the interview process, of course. Pretty sure indexes are basic things you learn when setting up your database schema, and most ORMs provide very easy way to do that and go over it in their getting started section. They usually have indexes by default for ID fields and foreign key fields. I had no problems understanding having to add indexes to often queried fields and the trade off for having too many indexes. When I started learning how to actually use something like MySQL I had no clue what data structure indexes used underneath, but the concept itself is fairly simple compared to how b-tree works. The vendors you have met have been incompetent for some other reason as opposed to not knowing data structures.