You want to practice some SQL? So here is a list of differents sites to practices your skills

Datalemur

It contains a lot of challenges not only related with sql but also with probability, python, machine learning and others.

Leetcode

As one of the platform for coding interview preparation, leetcode has some interesting challenge, one that I just recently complete is the SQL 50, and because I like the challenge is the reason for me to recommend leetcode for sql site for practicing.

HackerRank

Another popular one, has really good amount of problems related with sql, nice UI, so maybe give a try in case leetcode or datalemur are not of your taste.

Conclusion

I think this are a really good starting point websites to start our journey with sql. In the future I will post more sites related with sql.