Several tables have 'rank' columns which in some cases are not nullable. What are they for? - Mark Mark Schreiber Principal Scientist (Bioinformatics) Novartis Institute for Tropical Diseases (NITD) 10 Biopolis Road #05-01 Chromos Singapore 138670 www.nitd.novartis.com phone +65 6722 2973 fax +65 6722 2910