third edition of SQL FOR SMARTIES

I am getting ready to do the third edition of SQL FOR SMARTIES this
month.  If anyone has an SQL programming technique, trick or tip that
they would like to see in the book, drop me an email.

You get a virtual beer and your name in the book.  Even better, if you
have an improvement on something in the second edition, you get two
virtual beers and a chance to humilate me in my own book!

I know that this is not exactly the newsgroup for Standard SQL
programming, but you guys seem to reference the book fairly often in
postings.  I am looking for code that is Standard SQL-92 or higher,
but if you do not know Standard SQL, then use poprietary code that
maps into Standard SQL (the most common example would be temporal
functions) or it should be portable (i.e. The MOD() function is not
part of SQL-92, but every SQL product has some version of it).