Even though the post above is a decade old now, it's still a great recommendation. I can't speak to the first link with any knowledge because this is the first time I've seen it but I have confirmed that the link still works, as does the second.
The second link is what I normally refer beginners to with the understand that it covers MANY different SQL RDBMS engines and not just Microsoft SQL Server/T-SQL. That can be an advantage and a disadvantage because it's not always totally clear on which engine is being used for some of the demos. There's a lot of "common" SQL known as ANSI SQL but almost none of the engines follow pure ANSI SQL.
They DO have different sections for the different functions of each RDBMS, though. And virtually every page has a "Try It" section where you can write a query and see what is returned.