I am trying to get a more than superficial level of knowledge on deploying services on relational databases with a lot of traffic. I don't know if it makes sense to grab any manual of a relational database, like PostgreSQL or MySQL, or if that is too specific and it makes more sense to start with a more general book. [Please do not suggest Designing Data Intensive Applications, I am already reading it :) ] Moreover, what are the best resources you know of that you used to learn SQL queries and their syntax properly? Thank you very much!