https://www.reddit.com/r/learnprogramming/comments/sssdw8/alternatives_to_leetcode/
https://edabit.com/challenges/javascript (Python & Javascript)
https://www.techiedelight.com/ (C++, Java, Python)
https://www.geeksforgeeks.org/
https://www.geeksforgeeks.org/sql-tutorial/?ref=lbp
https://www.hackerrank.com/domains/sql
https://www.interviewbit.com/courses/databases/sql-queries/
https://open.kattis.com/languages (Python, etc..)