These are all my answers from PGEXERCISES.COM written in PostgreSQL. I went through and solved them all without looking at answers. These problems go from the basic joins, aggregations, and timestamps to windows functions, recursion, and CTEs.
There is a png photo containing the schema of the database. The uploaded SQL files are grouped by subject.
https://www.pgexercises.com/ Here is the awesome website to get hands on practice and challenge yourself to learn PostgreSQL/SQL in general. Don't cheat yourself and look at the answers. Use StackExchange and other forums to get help with certain concepts. It takes about two weekends to complete.