This was my reason #1 to attend the UC and it lived up to my expectations!
The Lost art of the self join was a truly enjoyable experience. Beat Vontobel delivered with confidence and humor a talk about a subject that most people would consider dull.
It was a feast for all attendees with an inclination for hacking.
The truly amazing thing in this presentation was not that Beat explained how to solve a Sudoku puzzle with one query which is a truly amazing feat, but that he explained how to use the join mechanism to implement a backtracking machine, similar to a regular expression algorithm.
The presentation was concluded with a live solution of a 6x6 sudoku puzzle. The reason for not using a 9x9 puzzle is because MySQL has a limitation of 61 joins, and thus it can't solve the full puzzle.
At the end of the session, Beat delivered the punch line, and showed how the 9x9 puzzle can be solved with ... PostgreSQL!
That will be inspirational for MySQL developers. Bravo Beat!