SQL CASE QUERY FOR FINDING GREATER VALUE

SELECT        Marks_Entry_Details.*, Subject.MarkMax
FROM            Marks_Entry_Details INNER JOIN
                        Subject ON Marks_Entry_Details.Subject_Code = Subject.Subject_Code AND 
                        Marks_Entry_Details.Pattern_Code = Subject.PatternID COLLATE SQL_Latin1_General_CP1_CI_AS AND 
                        Marks_Entry_Details.Course_Code = Subject.CourseID COLLATE SQL_Latin1_General_CP1_CI_AS AND 
                        Marks_Entry_Details.Branch_Code = Subject.Branch_Code AND Marks_Entry_Details.Subject_Type = Subject.Sub_Type AND 
                        (case when ( Marks_Entry_Details.marks='AA' or  Marks_Entry_Details.marks='NA') then 0 else  Marks_Entry_Details.marks end)  > Subject.MarkMax
WHERE        (Marks_Entry_Details.Complete = 1) AND (Marks_Entry_Details.Pattern_Code IN ('ENGG_P2003', 'ENGG_P2008', 'ENGG_P2012'))