Left and Right Outer Joins

Outer joins can be split into two types:

Left outer joins
Right outer joins

Example:


SELECT ... 
FROM table1, table2 
...

If table1 contains a row with a null value in column1. To perform a left outer join, the WHERE clause is

WHERE table1.column1 = table2.column2 (+);

In a left outer join, the outer join operator is actually on the right of the equality operator.

If assume table2 contains a row with a null value in column2. To perform a right outer join:

WHERE table1.column1 (+) = table2.column2;


CREATE TABLE departments
(department_id             number(10)            not null,
 department_name           varchar2(50)      not null,
 CONSTRAINT departments_pk PRIMARY KEY (department_id)
);

insert into departments ( department_id, department_name )values(2,'Purchasing' );
insert into departments ( department_id, department_name )values(3,'Call Center' );
insert into departments ( department_id, department_name )values(4,'Communication' );

CREATE TABLE employees
( employee_id          number(10)      not null,
  last_name            varchar2(50)      not null,
  job_id               varchar2(30),
  department_id        number(10),
  salary               number(6),
  manager_id           number(6),
  CONSTRAINT           employees_pk PRIMARY KEY (employee_id),
  CONSTRAINT           fk_departments FOREIGN KEY (department_id) 
                       REFERENCES departments(department_id)
);
insert into employees( employee_id, last_name, job_id, salary,department_id ,manager_id)
values(                1001,        'Lawson',  'MGR',  30000, 1,             1004);
insert into employees( employee_id, last_name, job_id, salary, department_id ,manager_id)
values(                1002,        'Wells',   'DBA',  20000, 2,             1005 );
insert into employees( employee_id, last_name, job_id, salary, department_id ,manager_id)
values(                1003,        'Bliss',   'PROG', 24000, 3,             1004);
insert into employees( employee_id, last_name, job_id, salary, department_id, manager_id)
values(                1004,        'Kyte',    'MGR',  25000 ,4,             1005);
insert into employees( employee_id, last_name, job_id, salary, department_id, manager_id)
values(                1005,        'Viper',   'PROG', 20000, 1,             1006);
insert into employees( employee_id, last_name, job_id, salary, department_id,manager_id)
values(                1006,        'Beck',    'PROG', 20000, 2,             null);
insert into employees( employee_id, last_name, job_id, salary, department_id, manager_id)
values(                1007,        'Java',    'PROG', 20000, 3,             1006);
insert into employees( employee_id, last_name, job_id, salary, department_id, manager_id)
values(                1008,        'Oracle',  'DBA',  20000, 5,             1006);


SQL> select e.employee_id, e.last_name, d.department_name
  2  from employees e, departments d
  3  where e.department_id = d.department_id(+)
  4    and e.job_id = 'MGR';

EMPLOYEE_ID LAST_NAME             DEPARTMENT_NAME
----------- --------------------------------------------------
       1004 Kyte                    Communication


SQL>
SQL> select e.employee_id, e.last_name, d.department_name
  2  from employees e, departments d
  3  where e.department_id(+) = d.department_id
  4    and e.job_id = 'MGR';

EMPLOYEE_ID LAST_NAME            DEPARTMENT_NAME
----------- --------------------------------------------------
       1004 Kyte                 Communication