If you're running into performance problems, knowing those things isn't enough. You need to know about query plans, different complexities of each kind of join algo, etc as well as how to get the query plan, how to profile your database query, etc. Basically databases are hard and you probably will need more than basic theory for anything that is more than a low-traffic CRUD app with latency SLAs on the order of hundreds of milliseconds or more.
This isn’t rocket science either. The theory behind database optimization is basically the same across every RDMS I’ve ever used (SQL server, Postgres, MySQL, and to a lesser extent Redshift). The second thing I learned about databases is how to look at a query plan and how to optimize it.
Why wouldn’t a developer’s job be to learn how to optimize a database query but would be to learn how to optimize a program?
I didn't claim it was rocket science nor that developers shouldn't learn these skills; only that optimizing a database is out of bounds of what most would consider "basic relational database theory". But beyond that, lots of developers aren't interfacing with a relational database. In a past life, I worked on embedded electronics. Other people work on operating systems. Others specialize in compilers or graphics or etc. Databases are a good skill to have, but it doesn't mean everyone should train like a web app dev either.
