> I was thinking about getting Oracle certified for SQL (which costs 2.5k)
No, it doesn't. Maybe if you take one of those week-long classes. But the books for the SQL Fundamentals and Administration 1 exams are about $30 each, and the two tests are about $200/each.
The SQL Fundamentals book is great for learning SQL, even if you don't go for the cert.
You could buy the Oracle 1Z0-061(?) SQL Fundamentals Exam prep book and follow it through.
https://smile.amazon.com/Oracle-Database-Fundamentals-Guide-1Z0-061/dp/0071820280/