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- PostgreSQL 教程
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PostgreSQL 语法
- PostgreSQL 运算符
- PostgreSQL SELECT
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- PostgreSQL ORDER BY
- PostgreSQL LIMIT
- PostgreSQL MIN and MAX
- PostgreSQL COUNT
- PostgreSQL SUM
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- PostgreSQL LIKE
- PostgreSQL IN
- PostgreSQL BETWEEN
- PostgreSQL AS
- PostgreSQL Joins
- PostgreSQL INNER JOIN
- PostgreSQL LEFT JOIN
- PostgreSQL RIGHT JOIN
- PostgreSQL FULL JOIN
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- PostgreSQL UNION
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- PostgreSQL HAVING
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- 练习
PostgreSQL 内连接
内部联接
这个INNER JOIN关键字选择在两个表中具有匹配值的记录。
让我们看一个使用我们的虚拟对象的例子testproducts表格：
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)
我们将努力加入testproducts表与categories表格：
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)
请注意，许多产品testproducts有一个category_id与中的任何类别都不匹配categories表格。
通过使用INNER JOIN我们不会获取不匹配的记录，我们只会获取匹配的记录两个都表：
示例
加入testproducts到 categories使用category_id柱子：
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
仅返回两个表中都匹配的记录：
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 rows)
笔记：JOIN和INNER JOIN会给出相同的结果。
INNER是默认的连接类型JOIN，所以当你写JOIN解析器实际上写的是INNER JOIN。
PostgreSQL 练习
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