I just finished learning Postgres! I used codecademy's SQL session for the intro, but then just decided to play around with queries. This diagram was my most useful resource, and one that I still look at on a daily basis when trying to create queries - I hope it helps! https://www.sqlite.org/images/syntax/select-stmt.gif
I also look at the postgres docs very frequently for syntax and format and those help me a lot. Stack Overflow is also a great resource!