[crease]

What topics/ideas would say someone needs to understand in order to really understand relational databases? Also, can you recommend any resources?

[Mister_Snuggles]

I don't have any good resources on the data modeling side, but on the SQL side the PostgreSQL manual[0] is really good. Even when I'm working with an Oracle database, I often find myself looking at the PostgreSQL documentation.

[0] https://www.postgresql.org/docs/12/index.html