Sql 通过未按预期运行进行分组

假设我有三个表——Orders、OrderDetails和ProductType——Orders表包含一列Customer。我需要做的是编写一个查询，显示客户列表和每个客户下了多少订单，并按另一列显示和分组，这是一个布尔值，基于特定类型的产品（如电话）是否在订单中

例如，我们可能有：

客户| NumOrders |包括电话

---------------------------------

詹姆逊| 3 |是

史密斯| 5 |是

韦伯| 1 |是

亚当斯| 2 | |否

詹姆逊| 1 |否

史密斯| 7 |否

韦伯| 2 |否

然而，当我尝试为此编写查询时，我得到了多行，其中Customer和IncludesPhone的值相同，NumOrders的值各不相同。为什么会这样？我的问题如下：

从订单中选择客户，将（客户）计算为NumOrders，在（ProductType.Type='Phone'）时按大小写，然后选择“是”或“否”作为includephone
结束内部加入订单详细信息内部加入产品类型
按客户分组，键入
按includephone订购，客户

由于您同时对

客户

和

类型

进行分组，因此您的查询将返回每种类型每名客户的订单数量。如果每个客户只需要一行，则应仅按

客户

分组，然后使用类似的方法确定某个客户是否购买了手机：

SELECT Customer, COUNT(Customer) AS NumOrders, 
    CASE 
        WHEN SUM(CASE WHEN (ProductType.Type = 'Phone') THEN 1 ELSE 0 END) > 0 
        THEN 'Yes' 
    ELSE 'No' END AS IncludesPhone
FROM Orders INNER JOIN OrderDetails INNER JOIN ProductType
GROUP BY Customer
Order By IncludesPhone, Customer

---

内部总和基本上计算每个客户购买的手机数量。如果大于0，则客户至少购买了一部手机，我们返回“是”。

由于您同时对

客户

和

类型

进行分组，因此您的查询将返回每个客户每种类型的订单数。如果每个客户只需要一行，则应仅按

客户

分组，然后使用类似的方法确定某个客户是否购买了手机：

SELECT Customer, COUNT(Customer) AS NumOrders, 
    CASE 
        WHEN SUM(CASE WHEN (ProductType.Type = 'Phone') THEN 1 ELSE 0 END) > 0 
        THEN 'Yes' 
    ELSE 'No' END AS IncludesPhone
FROM Orders INNER JOIN OrderDetails INNER JOIN ProductType
GROUP BY Customer
Order By IncludesPhone, Customer

---

内部总和基本上计算每个客户购买的手机数量。如果大于0，则客户至少购买了一部手机，我们返回“是”。

这是因为您按

类型

列进行分组，因此可能存在重复行。例如，对于类型“Email”和“Personal”列

includePhone

将为“No”，但当您按

Type

分组时，输出中将有两条记录

要解决此问题，可以在

group by

子句中使用相同的表达式，或使用子查询或：

在

group by

子句中使用相同的表达式：

select
    Customer,
    case when pt.Type = 'Phone' then 'Yes' else 'No' end as IncludesPhone,
    count(*) as NumOrders
from Orders as o
    inner join OrderDetails as od -- ???
    inner join ProductType as pt -- ???
group by Customer, case when pt.Type = 'Phone' then 'Yes' else 'No' end

---

这是因为您按

类型

列进行分组，所以可能会有重复的行。例如，对于类型“Email”和“Personal”列

includePhone

将为“No”，但当您按

Type

分组时，输出中将有两条记录

要解决此问题，可以在

group by

子句中使用相同的表达式，或使用子查询或：

在

group by

子句中使用相同的表达式：

select
    Customer,
    case when pt.Type = 'Phone' then 'Yes' else 'No' end as IncludesPhone,
    count(*) as NumOrders
from Orders as o
    inner join OrderDetails as od -- ???
    inner join ProductType as pt -- ???
group by Customer, case when pt.Type = 'Phone' then 'Yes' else 'No' end

将组更改为

GROUP BY    Customer, 
            CASE WHEN (ProductType.Type = 'Phone') THEN 'Yes' ELSE 'No' END

将组更改为

GROUP BY    Customer, 
            CASE WHEN (ProductType.Type = 'Phone') THEN 'Yes' ELSE 'No' END

---

这个查询应该有效

SELECT Customer, COUNT(Customer) AS NumOrders, 
CASE WHEN (ProductType.Type = 'Phone') THEN 'Yes' ELSE 'No' END AS IncludesPhone
FROM Orders INNER JOIN OrderDetails INNER JOIN ProductType
GROUP BY    Customer, 
CASE WHEN (ProductType.Type = 'Phone') THEN 'Yes' ELSE 'No' END
Order By IncludesPhone, Customer

---

这个查询应该有效

SELECT Customer, COUNT(Customer) AS NumOrders, 
CASE WHEN (ProductType.Type = 'Phone') THEN 'Yes' ELSE 'No' END AS IncludesPhone
FROM Orders INNER JOIN OrderDetails INNER JOIN ProductType
GROUP BY    Customer, 
CASE WHEN (ProductType.Type = 'Phone') THEN 'Yes' ELSE 'No' END
Order By IncludesPhone, Customer

---

您可以尝试以下查询：

SELECT  x.Customer,x.NumOrders,
        CASE WHEN x.NumOrders>0 AND EXISTS(
            SELECT  *
            FROM    Orders o
            INNER JOIN OrderDetails od ON ...
            INNER JOIN ProductType pt ON ...
            WHERE   o.Customer=x.Customer
            AND pt.Type = 'Phone'
        ) THEN 1 ELSE 0 END IncludesPhone
FROM
(
    SELECT  Customer,COUNT(Customer) AS NumOrders
    FROM    Orders 
    GROUP BY Customer
) x
Order By IncludesPhone, x.Customer;

或者这个：

SELECT  o.Customer, 
        COUNT(o.Customer) AS NumOrders, 
        MAX(CASE WHEN EXISTS
        (
            SELECT  *
            FROM    OrderDetails od
            JOIN    ProductType pt ON ...
            WHERE   o.OrderID=od.OrderID -- Join predicated between Orders and OrderDetails table
            AND     ProductType.Type = 'Phone'
        ) THEN 1 ELSE 0 END) AS IncludesPhone
FROM    Orders o
GROUP BY Customer
ORDER BY IncludesPhone, o.Customer

---

您可以尝试以下查询：

SELECT  x.Customer,x.NumOrders,
        CASE WHEN x.NumOrders>0 AND EXISTS(
            SELECT  *
            FROM    Orders o
            INNER JOIN OrderDetails od ON ...
            INNER JOIN ProductType pt ON ...
            WHERE   o.Customer=x.Customer
            AND pt.Type = 'Phone'
        ) THEN 1 ELSE 0 END IncludesPhone
FROM
(
    SELECT  Customer,COUNT(Customer) AS NumOrders
    FROM    Orders 
    GROUP BY Customer
) x
Order By IncludesPhone, x.Customer;

或者这个：

SELECT  o.Customer, 
        COUNT(o.Customer) AS NumOrders, 
        MAX(CASE WHEN EXISTS
        (
            SELECT  *
            FROM    OrderDetails od
            JOIN    ProductType pt ON ...
            WHERE   o.OrderID=od.OrderID -- Join predicated between Orders and OrderDetails table
            AND     ProductType.Type = 'Phone'
        ) THEN 1 ELSE 0 END) AS IncludesPhone
FROM    Orders o
GROUP BY Customer
ORDER BY IncludesPhone, o.Customer

---

如果您使用OrderDetails加入订单，则COUNT将为您提供订购产品的数量，而不是订单的数量。这就是你所需要的？@BogdanSahlean-S.M的答案正是我所需要的。然后你的问题就错了：“我需要做的是写一个查询，显示客户列表以及每个客户下了多少订单”。您应该重新表述您的问题。如果您使用OrderDetails加入订单，则COUNT将为您提供订购产品的数量，而不是订单的数量。这就是你所需要的？@BogdanSahlean-S.M的答案正是我所需要的。然后你的问题就错了：“我需要做的是写一个查询，显示客户列表以及每个客户下了多少订单”。你应该重新表述你的问题。@AndriyM:我在GROUP BY中没有看到任何别名。请说得更具体一点。很显然，我看到了一些不存在的东西，对不起。@AndriyM:我在GROUP BY中没有看到任何别名。请说得更具体些。很明显我看到了一些不在那里的东西，对不起。