tricky query using NULLS

I've got a table called articleclass which contains meta data for one of my central tables. i've got a query which looks like this: select articles.sportsym,articles.articletype_id,author.templateid from articles,articleclass sport,articleclass atypeid,articleclassauthor where sport.templateid=atypeid.templateid and atypeid.templateid=author.templateid and (articles.author = author.author or atypeid.author is null) and (articles.sportsym = sport.sportsym or sport.sportsym is null) and (articles.articletype_id = atypeid.number or atypeid.number is null) What I'm trying to get to is a mechanism wihch will return the template based on the meta-data. I am trying to table-ize these rules so that I can adminster them better than the 10000 lines of perl code does now. As you can see, the 'or XXXXX is null' clause is rather tricky. Am I making a bad move here? Can someone suggest a better approach? The query almost works - its that almost part that bugs me. BX 1 t.SportsBahr CB 3 99t.articles CB 3 99t.articles CB 3 99t.articles CB 3 99t.articles notice that it correclty returns the template for the sportsbahr, but the 99t.articles I think is a cartesian product due to the NULLs in the sportsym column in the articleclass table. Yet I'd like to keep these to represent the 'ALL SPORTS' condition. I realize that this email is long and drawn out, but anyone has an idea of a direction here, it'd be great. Thanks for your time. David Buttrick The Sporting News