SQL Server Code,Tips and Tricks, Performance Tuning

There is a puzzle on LessThanDot

The goal is to identify all friday the thirteenths for a given timeframe. We'll use a relatively small number of years, like 10. This should make it a little easier in procedural languages.

I posted my SQL solution, what about you?

Go here: Friday the Thirteenths and show me what you got. Make sure to use the [hide][/hide] tags so you don't spoil it for other people

ComputerWorld has posted three SQL puzzles that were written by Joe Celko on their website. These puzzles come from Joe Celko's latest book Joe Celko's SQL Puzzles and Answers, Second Edition

These are the puzzles:
Puzzle 1: FISCAL YEAR TABLES
Answer #1
Puzzle 4: SECURITY BADGES
Answer #1
Answer #2
Puzzle 9: AVAILABLE SEATS
Answer #1
Answer #2
Answer #3
Answer #4
Answer #5

the site has individual links to each puzzle and answer, the link to the puzzles is here: http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9012350&source=NLT_APP&nlid=48
Let me know what you think and if you can come up with better/different answers.