SQL Skills You Need: Filter, Join, and Summarize Any Table
Six SQL tools carry almost every real question you'll ask a database: WHERE, JOIN, GROUP BY, CASE, subqueries, and window functions. This guide builds a three-question mental model, then works through all six on a small community book-swap database you can reproduce yourself.
July 11, 2026 in SQL by Mehdi Lotfinejad15 minutes