Question

我有三张表格，内容如下。

表1：产品 - 列：产品名称，价格，产品ID

表2：客户 - 列：客户名称，客户ID，城市

表3：订单 - 列：订单ID，客户ID，产品ID

以下情景的查询应该是什么？

方案：需要显示客户名称，各个客户的订单号，支付总价（各客户的所有订单总和）。

Answer 1

尝试类似

的内容

SELECT c.CustomerName,
    count(o.orderId) [Orders Count],
    SUM(p.Price) [Total Price]
FROM CUSTOMERS c
    JOIN ORDERS o ON o.customer_id = c.customer_id
    JOIN PRODUCTS p ON p.product_id = o.product_id
GROUP BY c.CustomerName

Answer 2

试试这个：

SELECT c.name,COUNT(o.id),SUM(p.price)
FROM customers c
INNER JOIN orders o ON c.id = o.customer_id
INNER JOIN products p ON p.id = o.product_id
GROUP BY c.name;

您通过customer_id与订单一起加入客户;然后使用product_id与产品加入订单。

然后您只需GROUP BY c.name获取每个客户的COUNT（o.id）和SUM（p.price）的聚合值。

Answer 3

以下内容如何：

SELECT c.[Customer Name], COUNT(DISTINCT o.[Order ID]), SUM(p.Price)
FROM Customers AS c
JOIN Orders AS o ON c.[Customer ID] = o.[Customer ID]
JOIN Products AS p ON o.[Product ID] = p.[Product ID]
GROUP BY c.[Customer Name]

唯一的问题是，Orders表似乎缺少Quantity字段。所以，在上面的例子中，我只是在总结价格。

另外，为了获得每个客户的订单数量，我在COUNT（）函数中使用了distinct。如果单个订单可以指向多个产品，则需要执行此操作。否则你可以删除它。

Answer 4

试试这个：

select c.customer_name, x.no_of_orders, y.total_price from customer c
left join (
    select customer_id, COUNT(customer_id) as no_of_orders from orders 
    group by customer_id) x on c.customer_id = x.customer_id
left join (
    select o.customer_id, SUM(p.price) as total_price from order o 
    inner join products p on o.productid = p.productid
    group by customer_id) y on c.customer_id = y.customer_id

当有多个WHERE语句时如何计数

4 个答案: