Where clause in cursor

Question

I often have a problem with cursors and after playing around they usually work. The problem is I don't really know what I'm doing as I'm relativly new to all this! Perhaps someone can help ;)
I have the folling code to test my cursor:
declare
vcrn varchar2(8) := :module_choice.crn;
vgroup_code varchar2(10) := :module_choice.group_code;
vclass_type varchar2(10) := :module_choice.class_type;
i int := 0;
cursor att_cur is
select student_id, attended, notes
from attendance_register
where crn = vcrn ;
AND group_code = vgroup_code
AND class_type = vclass_type;
BEGIN
for row in att_cur loop
     i := i + 1;
end loop;
message(i);
END;
the message shows i = 0, but I know it's not. When I comment out the where clause it works.
I guess my real question would be how do you get a where clause to work like this??
Thanks in Advance
Mark

Answer 1

This where clause will succeed if some of the variables are null:
where ( crn = vcrn or vcrn is null )
  AND (group_code = vgroup_code or vgroup_code is null)
  AND (class_type = vclass_type or vclass_type is null)But I am very concerned about your Char datatypes. Those trailing spaces will give you nothing but lots of grief. Unless you have a compelling reason to keep them, they should be changed to varchar2.