Jonathan Lewis and Visual SQL Tuning
Sometimes, it is a great idea to push away the keyboard when tackling the problems of an ill-performing, complex, query, and take up pencil and paper instead. By drawing a diagram to show off all the tables involved, the joins, the volume of data involved, and the indexes, you’ll see more easily the relative efficiency of the possible paths that your query could take through the tables.
— Jonathan Lewis
Check out Jonathan’s insightful article on the power of graphically representing a SQL statement to help identify efficiencies and inefficiencies in a SQL query: