Sql Select 来自多个 table

Question

我有 3 个 table：

Visitor table
VisitorId (pk)
Name
Phone


Country table
CountryId (pk)
Name
Code

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

我想让每个国家/地区在 Travels table 中创建另一个入口，其中将包含 CountryId、VisitorId 和 false IsVisited.

更新

INSERT INTO Travels (CountryId, VisitorID, IsVisisted)
SELECT Visitor.VisitorId, Country.CountryId, 1 FROM Visitor, Country

Answer 1

你应该写成：

-- 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

否则，如果您想为 Country 和 Visitor 中的每个组合创建一个条目，请写为：

-- 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

Sql Select 来自多个 table

Sql Select From multiple table

c#

sql

tsql

sql-server