[SQL] LEFT Outer Join, RIGHT Outer Join, FULL Outer Join

일반적으로는 Inner Join 즉 테이블의 교집합을 Join하지만 join하는 다른 테이블에 데이터가 없더라도 join을 하여 데이터를 얻어 오도록 하는 것이 outer join입니다.

 

Outer Join에는 다음과 같이 세 가지가 있습니다. LEFT, RIGHT, FULL Outer Join

 

LEFT OUTER JOIN

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;

https://www.w3schools.com/sql/sql_join_left.asp

SQL LEFT JOIN Keyword

 

RIGHT OUTER JOIN

SELECT Orders.OrderID, Employees.LastName, Employees.FirstName
FROM Orders
RIGHT JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
ORDER BY Orders.OrderID;

https://www.w3schools.com/sql/sql_join_right.asp

SQL RIGHT JOIN Keyword

 

FULL OUTER JOIN

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
FULL OUTER JOIN Orders ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;

https://www.w3schools.com/sql/sql_join_full.asp

SQL FULL OUTER JOIN Keyword