CREATE PROCEDURE [dbo].[BillingCalculateInterview]
  @UserID int,
  @ProjectID int,
  @date1 datetime,
  @date2 datetime,
  @Count int = null output,
  @SuccessCount int = null output
AS

-- проверяем чтобы даты не были больше текущей
if (@date2 > GETDATE())
  set @date2 = GETDATE()

if (@date2 < @date1)
begin
  set @count = null
  set @successcount = null
  return
end

set nocount on

-- считаем
select
  @count = count([ID]),
  @successcount = sum(case when [iv_IsSuccess] = 1 then 1 else 0 end)
from
  [Billing] with (nolock)
where
  (@userid is null or [UserID] = @userid) and 
  (@projectid is null or [ProjectID] = @projectid) and 
  [EventTypeID] = 20 and 
  ([PeriodDT2] between @date1 and @date2)

if (@count = 0)
  set @count = null

set nocount off