Left Outer Join

El formato de la sintaxis para la clausula Left Outer Join es la siguiente:

SELECT tabla1.column, tabla2.column

FROM tabla1
LEFT OUTER JOIN tabla2
ON (tabla1.column = tabla2.column)

Un Left Outer Join desarrolla un inner join entre la tabla1 y la tabla2 basado en la condición  especificada después de la palabra ON. Cualquier fila de la tabla izquierda excluida por el inner join también será devuelta.

-- CONSULTA CON JOIN ON

SELECT d.department_id, d.department_name, d.manager_id, e.employee_id, e.first_name, e.last_name

FROM   departments d
       JOIN employees e ON (d.manager_id = e.employee_id)
ORDER BY d.department_id;      

-- CONSULTA CON LEFT OUTER JOIN

SELECT d.department_id, d.department_name, d.manager_id, e.employee_id, e.first_name, e.last_name
FROM   departments d
       LEFT OUTER JOIN employees e ON (d.manager_id = e.employee_id)
ORDER BY d.department_id;  

-- CONSULTA CON JOIN ON

SELECT d.department_id, d.department_name, e.employee_id, e.first_name
FROM   departments d
       JOIN employees e ON (d.department_id = e.department_id)
WHERE  d.department_name LIKE 'P%';      

-- CONSULTA CON LEFT OUTER JOIN ON

SELECT d.department_id, d.department_name, e.employee_id, e.first_name
FROM   departments d
       LEFT OUTER JOIN employees e ON (d.department_id = e.department_id)
WHERE  d.department_name LIKE 'P%';