PostgreSQL INNER JOIN
INNER JOIN
INNER JOIN 关键字会选择两个表中都具有匹配值的记录。
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)
请注意，testproducts 表中的许多产品具有 category_id，该 ID 在 categories 表中不匹配任何类别。
使用 INNER JOIN 时，不会返回没有匹配项的记录，只会返回同时匹配两个表的记录。
示例
使用 category_id 列将 testproducts 连接到 categories。
SELECT testproduct_id, product_name, category_name
FROM testproducts
INNER JOIN categories ON testproducts.category_id = categories.category_id;
运行示例 »
结果
仅返回两个表中都有匹配项的记录。
testproduct_id | product_name | category_name
----------------+------------------------+----------------
1 | Johns Fruit Cake | Confections
6 | Janes Favorite Cheese | Dairy Products
8 | Ellas Special Salmon | Seafood
9 | Roberts Rich Spaghetti | Grains/Cereals
(4 行)
注意： JOIN 和 INNER JOIN 的结果相同。
INNER 是 JOIN 的默认连接类型，因此当您编写 JOIN 时，解析器实际上会将其写为 INNER JOIN。
