UFN_RESERVATION_STARTDATETIME

CREATE function dbo.UFN_RESERVATION_STARTDATETIME
(
    @RESERVATIONID uniqueidentifier
)
returns datetime
as begin
    declare @STARTDATETIME datetime;

    select @STARTDATETIME = min(ITINERARYITEM.STARTDATETIME)
    from dbo.ITINERARYITEM
    inner join dbo.ITINERARY on ITINERARY.ID = ITINERARYITEM.ITINERARYID
    where ITINERARY.RESERVATIONID = @RESERVATIONID;

    if @STARTDATETIME is null
    begin
        select @STARTDATETIME = dbo.UFN_DATE_ADDHOURMINUTE(ARRIVALDATE, ARRIVALTIME)
        from dbo.RESERVATION
        where ID = @RESERVATIONID;
    end

    return @STARTDATETIME;
end