Knowing SQL and how relational databases actually work is one of the best superpowers a backend developer can have. If you want to go deeper than your database

Knowing SQL and how relational databases actually work is one of the best superpowers a backend developer can have. If you want to go deeper than your database manual, the best place is Andy Pavlo's db course, freely available at youtube. I don't write databases, but after watching it I understand trade-offs and performance considerations much better, and feel much more comfortable reading Postgresql manual.