Duplicates And The GROUP BY Clause

I am making a website where users go to a page that lists every Program in their area. The first time the page loads they see all the Programs, then then can filter it down with drop down lists. I have everything working except for the Category because some programs have more than one category. The select is working good but I get duplicates.





Here it is:





SELECT DISTINCT


p.ProgramID,


p.ProgramName,


p.ProgramCity,


p.ProgramState,


p.ProgramCountyID,


p.ProgramHours,


p.ProgramContactName,


p.ProgramPhone,


p.ProgramEmail,


p.ProgramGrades,


p.ProgramTransportation,


pc.ProgramID,


pc.CategoryID





FROM


Programs p,


ProgramCategories pc





WHERE


p.ProgramCountyID IS NOT NULL AND


p.ProgramCity IS NOT NULL AND


p.ProgramHours IS NOT NULL AND


p.ProgramGrades IS NOT NULL AND


p.ProgramTransportation IS NOT NULL AND


p.ProgramID = pc.ProgramID AND


pc.CategoryID IS NOT NULL








GROUP BY


p.ProgramID





ORDER BY


p.ProgramName ASC











When I have just p.ProgramID in the GROUP BY clause, I get the error:





"column name" is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.





But when I put all the column names in the GROUP BY clause, I still get duplicates. What can I do to stop this. When the user selects a category the pc.CategoryID IS NOT NULL changes to pc.CategoryID = 3 (or whatever they select) and everything works the way its supposed to. I just want each individual program to show only once when the page first loads.





Thanks for your time


Dave