PostgreSQL RIGHT JOIN
RIGHT JOIN
The RIGHT JOIN keyword selects ALL records from the "right" table,
and the matching records from the "left" table.
The result is 0 records from the left side if there is no match.
Let's look at an example using our dummy testproducts table:
----------------+------------------------+-------------
1 | Johns Fruit Cake | 3
2 | Marys Healthy Mix | 9
3 | Peters Scary Stuff | 10
4 | Jims Secret Recipe | 11
5 | Elisabeths Best Apples | 12
6 | Janes Favorite Cheese | 4
7 | Billys Home Made Pizza | 13
8 | Ellas Special Salmon | 8
9 | Roberts Rich Spaghetti | 5
10 | Mias Popular Ice | 14
(10 rows)
We will try to join the testproducts table
with the categories table:
-------------+----------------+------------------------------------------------------------
1 | Beverages | Soft drinks, coffees, teas, beers, and ales
2 | Condiments | Sweet and savory sauces, relishes, spreads, and seasonings
3 | Confections | Desserts, candies, and sweet breads
4 | Dairy Products | Cheeses
5 | Grains/Cereals | Breads, crackers, pasta, and cereal
6 | Meat/Poultry | Prepared meats
7 | Produce | Dried fruit and bean curd
8 | Seafood | Seaweed and fish
(8 rows)
Note: Many of the products in testproducts have a
category_id that does not match any of the
categories in the categories table.
By using RIGHT JOIN we will get all
records from categories, even the ones with no
match in the testproducts table:
Example
Join testproducts to
categories using the category_id column:
FROM testproducts
RIGHT JOIN categories ON testproducts.category_id = categories.category_id;
Result
All records from categories, and only the matched records from
testproducts:
----------------+------------------------+----------------
1 | Johns Fruit Cake | Confections
6 | Janes Favorite Cheese | Dairy Products
8 | Ellas Special Salmon | Seafood
9 | Roberts Rich Spaghetti | Grains/Cereals
| | Condiments
| | Meat/Poultry
| | Beverages
| | Produce
(8 rows)
Note: RIGHT JOIN and
RIGHT OUTER JOIN
will give the same result.
OUTER is the default join type for
RIGHT JOIN, so when you write
RIGHT JOIN the parser actually writes
RIGHT OUTER JOIN.