PostgreSQL outer join

Left outer join: a 기준으로 다 나옴

SELECT 
    a.id AS table_a_id, 
    a.name AS table_a_name, 
    b.id AS table_b_id, 
    b.description AS table_b_description
FROM table_a a
LEFT OUTER JOIN table_b b ON a.id = b.a_id;

table_a_id | table_a_name | table_b_id | table_b_description
-----------+-------------+------------+----------------------
1          | Apple       | 1          | Fruit
2          | Carrot      | NULL       | NULL
3          | Orange      | 3          | Citrus

Right outer join: b 기준으로 다 나옴

SELECT 
    a.id AS table_a_id, 
    a.name AS table_a_name, 
    b.id AS table_b_id, 
    b.description AS table_b_description
FROM table_a a
RIGHT OUTER JOIN table_b b ON a.id = b.a_id;

table_a_id | table_a_name | table_b_id | table_b_description
-----------+-------------+------------+----------------------
1          | Apple       | 1          | Fruit
NULL       | NULL        | 2          | Vegetable
3          | Orange      | 3          | Citrus

Full outer join: 양쪽 다 나옴

SELECT 
    a.id AS table_a_id, 
    a.name AS table_a_name, 
    b.id AS table_b_id, 
    b.description AS table_b_description
FROM table_a a
FULL OUTER JOIN table_b b ON a.id = b.a_id;

table_a_id | table_a_name | table_b_id | table_b_description
-----------+-------------+------------+----------------------
1          | Apple       | 1          | Fruit
2          | Carrot      | NULL       | NULL
3          | Orange      | 3          | Citrus
NULL       | NULL        | 2          | Vegetable