[GENERAL] zero length string to zero

[Shadi Mal]

Hi,
 I get zero length string in my result but I want to have zero value
instead.
what can I do?
my query is:
SELECT unreadmandatory.id,
         Count(unreadmandatory.course) AS nbrofmandatoryleft
           FROM unreadmandatory
          GROUP BY unreadmandatory.id