I just launched a new free SQL practice platform today called DataLemur! I'm the author of Ace the Data Science Interview, and a lot of our readers wanted to practice the SQL questions from the book, so we decided to make DataLemur free and open!<p>Even if you aren't job hunting, these tricky SQL questions are pretty fun to practice on.
if you like playing around with data using SQL you might also like my sql-examples repository on github (<a href="https://github.com/SimonWaldherr/sql-examples" rel="nofollow">https://github.com/SimonWaldherr/sql-examples</a>).
There is an online SQL editor (based on SQLite) with example queries. Feel free to expand the project and add new examples. Pull requests are welcome.
Nice one. How do you decide the difficulty of each problem? One hard problem seemed easy using analytic functions while a medium problem felt hard as it required a self-join the realization of which is the harder part.