Setting A MySQL Column to NO DUPLICATES

Does anyone know how to set a column in a MySQL table to disallow any duplicate entries. I've already got a PRIMARY KEY defined for this table. I tried setting the other field to a MUL KEY, hoping that it would not permit duplicates, but it does. I've searched the MySQL docs without success. I wish their site was a good as PHP.net. Later, Jeff Ganaway ___________________________________________________________ Save 15% on 2002 Calendars and Holiday Cards! http://www.AvantGifts.com Discount Code: hopper22ct Offer Good Through October 31, 2001 ___________________________________________________________