I resolved all the database questions on Leetcode.com recently. The questions cover most of the SQL common queries inlcuding JOIN, Ranking and other SQL basics. I provided the answers as well as explanations in this blog, as a way to consolidate the SQL knowledge.

The questions on Leetcode only support MySQL, so you can install MySQL on your laptop for testing purpose before submitting the solution, or use online SQL platforms to test you query. E.g. rextester more ...