PostgreSQL FULL JOIN
FULL JOIN
FULL JOIN 关键字选择两个表中的所有记录，即使没有匹配项。对于匹配的行，两个表中的值都可用；如果不存在匹配项，则空字段将获得 NULL 值。
让我们看一个使用我们的模拟 testproducts 表的示例
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 行)
我们将尝试将 testproducts 表与 categories 表连接。
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 行)
注意：testproducts 中的许多产品都有一个 category_id，它与 categories 表中的任何类别都不匹配。
通过使用 FULL JOIN，我们将获得 categories 表和 testproducts 表中的所有记录。
示例
使用 category_id 列将 testproducts 连接到 categories。
SELECT testproduct_id, product_name, category_name
FROM testproducts
FULL JOIN categories ON testproducts.category_id = categories.category_id;
运行示例 »
结果
将返回两个表中的所有记录。
没有匹配项的行将在另一个表中的字段中获得 NULL 值。
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)
注意： FULL JOIN 和 FULL OUTER JOIN 的结果相同。
OUTER 是 FULL JOIN 的默认连接类型，因此当您编写 FULL JOIN 时，解析器实际上会写入 FULL OUTER JOIN。
