In many of my articles, I mention that SQL involves a lot of logic and that you can improve your SQL querying capabilities by solving pure logic puzzles. You've probably already heard of the logic puzzle called Sudoku, which is popular these days.

Sudoku is a Japanese term that refers to a number that's singular or unique. However, the concept behind Sudoku puzzles is by no means unique. In 1783, Swiss mathematician Leonhard Euler invented Latin squares as a variation of magic squares. In L...