CREATE FUNCTION erFullur(@Bnr VARCHAR(5), @Ferd INT)
RETURNS INT
AS
BEGIN
   IF(
        SELECT COUNT(*)FROM FerdamennBilar
        WHERE Bnr = @Bnr AND FBFerd = @Ferd
   )>=
   (
        SELECT Bsaetafjoldi FROM Bilar WHERE Bnr = @Bnr
   ) RETURN 1
   RETURN 0
END

CREATE PROCEDURE skraFiBil(@Fnr INT, @Bnr VARCHAR(5), @Ferd INT)
AS
BEGIN
  IF dbo.erFullur(@Bnr, @Ferd)<> 0
     raiserror('Bíllinn er fullur',11,1)
  ELSE
     INSERT INTO FerdamennBilar(Fnr,Bnr,FBferd) VALUES(@Fnr,@Bnr,@Ferd)
END