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FULL JOIN

The FULL JOIN keyword selects ALL records from both tables, even if there is not a match. For rows with a match the values from both tables are available, if there is not a match the empty fields will get the value NULL.

Let's look at an example using our dummy testproducts table:

 testproduct_id |      product_name      | category_id
----------------+------------------------+-------------
              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:

 category_id | category_name  |                       description
-------------+----------------+------------------------------------------------------------
           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 FULL JOIN we will get all records from both the categories table and the testproducts table:

Example

Join testproducts to categories using the category_id column:

SELECT testproduct_id, product_name, category_name
FROM testproducts
FULL JOIN categories ON testproducts.category_id = categories.category_id;

Result

All records from both tables are returned.

Rows with no match will get a NULL value in fields from the opposite table:

 testproduct_id |      product_name       | category_name
----------------+-------------------------+----------------
              1 | Johns Fruit Cake        | Confections
              2 | Marys Healthy Mix       |
              3 | Peters Scary Stuff      |
              4 | Jims Secret Recipe      |
              5 | Elisabeths Best Apples  |
              6 | Janes Favorite Cheese   | Dairy Products
              7 | Billys Home Made Pizza  |
              8 | Ellas Special Salmon    | Seafood
              9 | Roberts Rich Spaghetti  | Grains/Cereals
             10 | Mias Popular Ice        |
                |                         | Condiments
                |                         | Meat/Poultry
                |                         | Beverages
                |                         | Produce
(14 rows)

Note: FULL JOIN and FULL OUTER JOIN will give the same result.

OUTER is the default join type for FULL JOIN, so when you write FULL JOIN the parser actually writes FULL OUTER JOIN.

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