What are some interesting SQL problems or query mistakes worth discussing?

[u/Due_Counter_2286]

I'm planning to share some SQL-related content on LinkedIn, but I want to avoid the usual beginner-level tutorials or generic interview questions.

I'm particularly interested in intermediate-level SQL concepts, window functions, CTEs, tricky query behavior, or situations where a query looks correct but produces unexpected results.

I'd love to hear from people working with SQL regularly.

What's an interesting SQL problem, subtle query mistake, or unexpected behavior you've encountered that made you think twice?

Looking for something technically meaningful that could spark a good discussion rather than another basic SQL tutorial.