[MSSQL] LEFT OUTER JOIN 예제

SELECT *

FROM Orders order by CustomerID

OrderID	CustomerID	EmployeeID	OrderDate	ShipperID
10308	2	7	1996-09-18	3
10365	3	3	1996-11-27	2
10355	4	6	1996-11-15	1
10383	4	8	1996-12-16	3
10278	5	8	1996-08-12	2

SELECT *

FROM Customers

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constituci� 2222	M�ico D.F.	05021	Mexico
3	Antonio Moreno Taquer�	Antonio Moreno	Mataderos 2312	M�ico D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK

두개를 LEFT OUTER JOIN 하게 되면

SELECT *

FROM Customers a

LEFT JOIN Orders b

ON a.CustomerID=b.CustomerID

ORDER BY Customers.CustomerName;

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country	OrderID	EmployeeID	OrderDate	ShipperID
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany	null	null	null	null
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constituci� 2222	M�ico D.F.	05021	Mexico	10308	7	1996-09-18	3
3	Antonio Moreno Taquer�	Antonio Moreno	Mataderos 2312	M�ico D.F.	05023	Mexico	10365	3	1996-11-27	2

결과에서 보면  LEFT OUTER JOIN 은 

ON CustomerID 를 기준으로 Orders 테이블과 일치하는 레코드가 없으면, Orders 테이블의 모든 컬럼이 담긴 row에 NULL을 넣는다