Great article. Very good primer on the subject. When you do your next one on advanced joins please talk about moving thing from the WHERE to the ON for better performance. Case in point I needed a list of all CUSTOMERs who had 'CREDIT' type ORDERs placed in the last 30 days. So instead of:

WHERE [ORDER].TypeId = 3 AND ...

use

INNER JOIN [ORDER] ON [ORDER].CustomerID = [CUSTOMER].Id AND [ORDER].TypeId = 3