If you also struggled to find open source database, JUST to practice simply queries link below will come you like light at the end of the tunnel. At least in my case was. After many tries to find open MySQL databases, ultimately I gave up. Luckily, I came across to this link somehow. And it helped me hugely, not only for making queries and joinings, but also from practising machine learning algorithms on relational datasets.
I hope this will help you too https://relational.fit.cvut.cz/search,
Enjoy!
Congratulations @sofija236! You received a personal award!
You can view your badges on your Steem Board and compare to others on the Steem Ranking
Vote for @Steemitboard as a witness to get one more award and increased upvotes!