https://www.kaggle.com/learn/intro-to-sql

https://www.kaggle.com/learn/advanced-sql

https://www.kaggle.com/datasets?fileType=sqlite

https://www.kaggle.com/datasets?fileType=bigQuery

https://www.databasestar.com/sql-practice/

Keep in mind that every database uses a common core of SQL but they are all using slightly different implementations of SQL. For example, SQLilte and bigQuery and MariaDB are likely to have very similar but slightly different syntax to accomplish the same task.

w3schools.com has a good SQL tutorial for beginners.

Have a look at SQLServerCentral.com. Lots of articles and forums there. Of some importance is to think about doing things in sets, not one by one. For example, if you need to do the same thing to a bunch of rows, don’t write a loop to do them one at a time - you can usually do them all at once. Lookup RBAR (Row By Agonising Row).

Here are some great sites for combined practice and learning:

https://sqlbolt.com/

https://8weeksqlchallenge.com/

https://sqlzoo.net/wiki/SQL_Tutorial

https://selectstarsql.com/

I'm no dev, but when I needed to learn SQL for work I found w3schools to be a great resource. They have guided lessons that are fairly well done and examples to practice the things they show. At the very least it may help reinforce concepts you learn in class and introduce you to some of the more complicated features of query construction ahead of time.

https://www.w3schools.com/sql/