C# Sql从多个表中选择

我有三张桌子：

Visitor table
VisitorId (pk)
Name
Phone


Country table
CountryId (pk)
Name
Code

Travels table
TravelId (pk)
CountryId (fk)
VisitorId (fk)
IsVisited (bool)

我希望每个国家都能创建另一个entrace in Travels表，该表将包含ISVISISTED的CountryId、VisitorId和false

更新

你应该这样写：

-- STEP2: Insert records:
INSERT INTO @Travels 
SELECT CountryId,VisitorId,0 FROM -- 0 = false for IsVisited
(
-- STEP1: first create a combination for all visitor Id and country Id 
-- and get all the combinations which are not there in existing Travels table
SELECT C.CountryId,V.VisitorId
FROM @Country C
CROSS JOIN @Visitor V
EXCEPT
SELECT CountryId,VisitorId
FROM @Travels
) AS T

-- STEP2: Insert records:
INSERT INTO @Travels 
SELECT  CountryId,VisitorId,0 FROM 
(
-- STEP1: first create a combination for all visitor Id and country Id 
SELECT C.CountryId,V.VisitorId
FROM @Country C
CROSS JOIN @Visitor V
) AS T

SELECT * FROM @Travels

否则，如果要为国家/地区和访客中的每个组合创建条目，请编写为：

-- STEP2: Insert records:
INSERT INTO @Travels 
SELECT CountryId,VisitorId,0 FROM -- 0 = false for IsVisited
(
-- STEP1: first create a combination for all visitor Id and country Id 
-- and get all the combinations which are not there in existing Travels table
SELECT C.CountryId,V.VisitorId
FROM @Country C
CROSS JOIN @Visitor V
EXCEPT
SELECT CountryId,VisitorId
FROM @Travels
) AS T

-- STEP2: Insert records:
INSERT INTO @Travels 
SELECT  CountryId,VisitorId,0 FROM 
(
-- STEP1: first create a combination for all visitor Id and country Id 
SELECT C.CountryId,V.VisitorId
FROM @Country C
CROSS JOIN @Visitor V
) AS T

SELECT * FROM @Travels

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