This is the article I remeber. It's a bit older too. I prefer the prolog solution!<p><a href="https://technology.amis.nl/2009/10/13/oracle-rdbms-11gr2-solving-a-sudoku-using-recursive-subquery-factoring/" rel="nofollow">https://technology.amis.nl/2009/10/13/oracle-rdbms-11gr2-sol...</a>