Aby bylo možné vrátit nebo vytvořit NULL
hodnoty budete muset použít LEFT JOIN
s.
Takže váš dotaz by měl být něco jako:
SELECT
a.ReservationStayID AS 'Reservation Id'
,a.PMSConfirmationNumber AS 'PMS No'
,a.CreatedOn AS 'Date Created'
,a.ArrivalDate AS 'Date of Arrival'
,a.DepartureDate AS 'Date of Departure'
,a.TAProfileID AS 'TA Id'
,a.StatusCode AS 'Status'
,b.PropertyCode AS 'Hotel'
,c.NAME AS 'Travel Agency'
,c.CountryCode AS 'Market Code'
,d.CountryName AS 'Mkt'
FROM ReservationStay a
INNER JOIN GuestStaySummary b ON a.ReservationStayID = b.ReservationStayID
LEFT JOIN TravelAgency c ON a.TAProfileID = c.TravelAgencyID
LEFT JOIN Market d ON c.CountryCode = d.CountryCode