Learning advanced SQL if I can't afford datalemur or stratascratch?

Looking to advance my sql skills.
I won’t give any certification exams, as they’re not worth having.
But I’ll read the books of those exams if they cover what I need.

I don’t need the administration part.
So, oracle certified associate is out of view. I looked at the syllabus of that exam and I already know most things and it’s basic.

I don’t need PL/SQL either.
So, oracle pl/sql is out of question.

I don’t either need python.

So, I need such a specific certification.

Tuning and performance optimization
Neither do I need this. I know I am being too specific.

Can you recommend anything for me? I want to practice real world problems.

I am already part of various foras like dba stackexchange etc. And read questions and try to answer. But it alone isn’t taking me anywhere.

Can you recommend some great sets of sql problems beyond the basics.

Do you think I should change my route, be flexible and learn pl/sql as well and give OCP?

I’ve already practiced problems from sqlzoo, sqlhack, sqlbolt bla bla.