Sql Query Optimization

You'd reach for it when a query is taking too long and you need to understand why, or when you're trying to figure out if an index is actually being used. It covers both PostgreSQL and MySQL, focuses on practical patterns like join optimization and subquery flattening, and includes the buffer analysis you need for real diagnostics. The approach is systematic rather than clever, which is exactly right for performance work. If you're comfortable reading query plans yourself, you might not need it, but it's solid for catching the common mistakes that slow down most applications.