I have this proc:

CREATE PROCEDURE bm_GetProjects
	@AppKey			int,
	@CategoryKey	int,
	@StatusKey		int

AS
BEGIN

	SELECT p.ProjectKey, p.ProjectName, p.ProjectCode, p.RateAmt, p.EstHours, p.EstStartDate,
		   p.EstEndDate, p.TotalHours, p.StartDate, p.EndDate, p.PercentDone,
		   p.CategoryKey, pc.CategoryName,
		   p.RateTypeKey, rt.TypeName AS RateTypeName,
		   p.StatusKey, psc.ProjectStatusCodeName AS StatusCode,
		   p.PriorityKey, pr.PriorityName AS Priority,
		   p.ManagerKey, LTRIM(RTRIM(e.LastName)) + ' ' + e.FirstName AS ManagerName
		FROM bm_Projects p
		JOIN bm_RateTypes rt ON rt.TypeKey = p.RateTypeKey
		JOIN bm_PrjCategories pc ON pc.CategoryTypeKey = p.CategoryKey
		JOIN bm_Priorities pr ON pr.PriorityKey = p.PriorityKey
		JOIN bm_ProjectStatusCodes psc ON psc.ProjectStatusCodeKey = p.StatusKey
		LEFT JOIN bm_Employees e ON e.EmployeeKey = p.ManagerKey
		WHERE p.AppKey = @AppKey AND
			  pc.CategoryTypeKey = @CategoryKey AND
			  psc.ProjectStatusCodeKey = @StatusKey
		ORDER BY ProjectName

END

It's possible for any combination of parameters to be passed. How do I change the WHERE clause to handle this?

Thanks