Question

I have this statement:

SELECT  COUNT(AccedentId) AS NumberOfAccedentInYear
            FROM         Accident
            GROUP BY DriverId, YEAR(AccedentDate)
            HAVING     (DriverId =@DriverId)<3

When there are rows, I get a valid count, but when there are no rows, the result is empty. I’d like the result to be 0 when there are no matching rows.

Answer 1

Maybe you wanted this (I’m keeping obvious syntax and spelling errors that I can’t really correct without more information):

SELECT NumberOfAccedentInYear = ISNULL
(
  (SELECT COUNT(AccedentId)
   FROM         Accident
   GROUP BY DriverId, YEAR(AccedentDate)
   HAVING     (DriverId =@DriverId)<3))
   , 0
);

For anyone curious about the COALESCE vs ISNULL discussion, and why I changed my answer to use ISNULL, @kanav rightly pointed out that COALESCE is more expensive. COALESCE evaluates the subquery twice, as I explained here: https://stackoverflow.com/a/10669660/61305