A RIGHT OUTER JOIN is one of the JOIN
operations that allow you to specify a JOIN clause. It preserves the
unmatched rows from the second (right) table, joining them with a NULL in
the shape of the first (left) table. A LEFT OUTER JOIN B is equivalent to
B RIGHT OUTER JOIN A, with the columns in a different order.
Syntax
TableExpression RIGHT [ OUTER ] JOIN TableExpression
{
ON booleanExpression |
USING clause
}
The scope of expressions in the ON clause includes
the current tables and any tables in query blocks outer to the current SELECT.
The ON clause can reference tables not being joined and does not have to
reference either of the tables being joined (though typically it does).
Example 1
-- get all countries and corresponding cities, including
-- countries without any cities
SELECT COUNTRIES.COUNTRY, CITIES.CITY_NAME
FROM CITIES
RIGHT OUTER JOIN COUNTRIES
ON CITIES.COUNTRY_ISO_CODE = COUNTRIES.COUNTRY_ISO_CODE
-- get all countries in Africa and corresponding cities, including
-- countries without any cities
SELECT COUNTRIES.COUNTRY, CITIES.CITY_NAME
FROM CITIES
RIGHT OUTER JOIN COUNTRIES
ON CITIES.COUNTRY_ISO_CODE = COUNTRIES.COUNTRY_ISO_CODE
WHERE Countries.region = 'Africa'
-- use the synonymous syntax, RIGHT JOIN, to achieve exactly
-- the same results as in the example above
SELECT COUNTRIES.COUNTRY, CITIES.CITY_NAME
FROM CITIES
RIGHT JOIN COUNTRIES
ON CITIES.COUNTRY_ISO_CODE = COUNTRIES.COUNTRY_ISO_CODE
WHERE Countries.region = 'Africa'
Example 2
-- a TableExpression can be a joinOperation. Therefore
-- you can have multiple join operations in a FROM clause
-- List every employee number and last name
-- with the employee number and last name of their manager
SELECT E.EMPNO, E.LASTNAME, M.EMPNO, M.LASTNAME
FROM EMPLOYEE E RIGHT OUTER JOIN
DEPARTMENT RIGHT OUTER JOIN EMPLOYEE M
ON MGRNO = M.EMPNO
ON E.WORKDEPT = DEPTNO
