SQL Server 查询：使用 JOIN 包含 NULL 值
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SQL Server Query: Using JOIN to include NULL values
提问by user3115933
I need help with the following SQL Server query where the columns a.TAProfileID and c.CountryCode have "NULL" values in the database.
我需要以下 SQL Server 查询的帮助，其中 a.TAProfileID 和 c.CountryCode 列在数据库中具有“NULL”值。
I want my JOIN statements to return "NULL" values where they exist.
我希望我的 JOIN 语句在它们存在的地方返回“NULL”值。
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
inner JOIN TravelAgency c ON a.TAProfileID = c.TravelAgencyID
inner JOIN Market d ON c.CountryCode = d.CountryCode
回答by Radu Gheorghiu
In order to return or produce NULLvalues you will have to use LEFT JOINs.
为了返回或生成NULL值，您必须使用LEFT JOINs。
So, your query should be something like:
所以，你的查询应该是这样的：
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
