数据库多表连接查询练习

**数据库多表连接查询练习**

在实际开发中，往往需要从多个表中获取数据，这时候就需要使用多表连接查询。下面我们将通过一个实例来演示如何进行多表连接查询。

**实例背景**

假设我们有三个表：`orders`、`customers` 和 `products`。

* `orders` 表包含订单信息，包括订单ID、客户ID、订单日期和总金额。
* `customers` 表包含客户信息，包括客户ID、客户名称和联系方式。
* `products` 表包含产品信息，包括产品ID、产品名称和价格。

**实例数据**

假设我们有以下数据：

sql-- orders 表+---------+-----------+------------+--------+
| order_id | customer_id | order_date | total |
+---------+-----------+------------+--------+
|1 |101 |2022-01-01 |100.0 |
|2 |102 |2022-01-15 |200.0 |
|3 |101 |2022-02-01 |150.0 |
+---------+-----------+------------+--------+

-- customers 表+---------+----------+---------------+
| customer_id | name | contact_info |
+---------+----------+---------------+
|101 | John |1234567890 |
|102 | Alice |9876543210 |
+---------+----------+---------------+

-- products 表+---------+-----------+--------+
| product_id | name | price |
+---------+-----------+--------+
|1 | Product A |50.0 |
|2 | Product B |100.0 |
|3 | Product C |200.0 |
+---------+-----------+--------+

sqlSELECT o.order_id,
 c.name AS customer_name,
 c.contact_info,
 p.name AS product_name,
 p.price,
 o.totalFROM orders oJOIN customers c ON o.customer_id = c.customer_idJOIN products p ON o.product_id = p.product_id;

sql+---------+---------------+---------------+-----------+--------+--------+
| order_id | customer_name | contact_info | product_name | price | total |
+---------+---------------+---------------+-----------+--------+--------+
|1 | John |1234567890 | Product A |50.0 |100.0 |
|2 | Alice |9876543210 | Product B |100.0 |200.0 |
|3 | John |1234567890 | Product C |200.0 |150.0 |
+---------+---------------+---------------+-----------+--------+--------+