JOINS and Venn Diagrams

I've been brushing up on probability, set theory, and statistics lately -- there's a lot of need for probability and stats at work and the set theory comes along with certification training and the math review.

Venn diagrams (an example of which is pictured to the left) are a fairly common way to represent sets and are used a lot in set theory -- and not coincidentally -- in database systems. (Relational databases are based on set theory!)

Today while I was helping out on database administrators stack exchange, I found a good link from Coding Horror that shows a bunch representing Venn diagrams of how JOINs work in SQL. The Venn diagrams themselves don't include the mathematical symbols from set theory, but they are useful nonetheless.