SQL Zoo is one of the few resources online that actually lets you build and run queries against existing tables. Each tutorial will show you a table and then have you run queries against it to answer specific questions. Some of the queries, particularly at first, are quite simple. They definitely get more challenging towards the end and can be real head scratchers.
This section contains helpful links to other content. It isn’t required, so consider it supplemental for if you need to dive deeper into something.