PostgreSQL INNER JOIN
INNER JOIN
INNER JOIN 關鍵字會選擇兩個表中都具有匹配值的記錄。
讓我們看一個使用我們的模擬 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)
我們將嘗試將 testproducts 表與 categories 表連線。
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)
請注意，testproducts 表中的許多產品具有 category_id，該 ID 在 categories 表中不匹配任何類別。
使用 INNER JOIN 時，不會返回沒有匹配項的記錄，只會返回同時匹配兩個表的記錄。
示例
使用 category_id 列將 testproducts 連線到 categories。
SELECT testproduct_id, product_name, category_name
FROM testproducts
INNER JOIN categories ON testproducts.category_id = categories.category_id;
執行示例 »
結果
僅返回兩個表中都有匹配項的記錄。
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 的結果相同。
INNER 是 JOIN 的預設連線型別，因此當您編寫 JOIN 時，解析器實際上會將其寫為 INNER JOIN。
