Counting number of joined rows in left join

Question

I\'m trying to write an aggregate query in SQL which returns the count of all records joined to a given record in a table; If no records were joined to the given record, the

Answer 1

You first want to count in your messaepart table before joining, i think. Try this:

   SELECT m.MessageId
        , COALESCE(c, 0) as myCount
     FROM MESSAGE m
LEFT JOIN (SELECT MESSAGEID
                , count(*) c 
             FROM MESSAGEPART 
            GROUP BY MESSAGEID) mp
       ON mp.MESSAGEID = m.MESSAGEID