You can do most anything with the wrong tool. I'd rather ask the question, when is PostgreSQL or MySQL the wrong tool for the job. I'm not sure I'm qualified to answer this, but I can point you in the direction of a book that has given me a much better understanding of the space. https://www.oreilly.com/library/view/designing-data-intensiv...
That said, I'll add MDN Web Docs [1] to the pile of links here as a good resource for practical details. If you're interested in the fundamentals of large-scale data-driven distributed systems (into which category many larger web applications fit), Designing Data-Intensive Applications [2] is quite excellent. NNGroup [3] has a lot of great foundational material on basic concepts of UX, usability, interaction, etc. for digital products.
[1] https://developer.mozilla.org/en-US/ [2] https://www.oreilly.com/library/view/designing-data-intensiv... [3] https://www.nngroup.com
https://www.oreilly.com/library/view/designing-data-intensiv...
That said, there are plenty of resources that have been helpful to me:
1) http://highscalability.com/
2) http://shop.oreilly.com/product/0636920032175.do
3) https://github.com/donnemartin/system-design-primer
Hope this helps!
Here's the table of contents: https://www.oreilly.com/library/view/designing-data-intensiv...
It seems to cover roughly the same areas and range as the book you mentioned, Database Systems: The Complete Book (2008). http://infolab.stanford.edu/~ullman/dscb.html