SQL Tutor
Unfortunately, this service has been hammered by people using VPNs to bypass the usage limits, making it expensive to maintain. So the free version is shutting down and access is limited to Data Elixir Pro subscribers.
Pro subscribers get topic-specific deep dives and access to our GPT-4o powered assistant that can help you find — and use — any topic from the newsletter over the past 5 years. It can help you with research, code development, SQL, data analysis, troubleshooting, and more.