如何使用GROUP BY子句选择

Question

我有任务。 ＆＃34;对于每个订单，输入订购的单位总数和客户的名称。＆＃34; 数据库：Microsoft SQL Server 12.0.2000.8 我到目前为止编写了这段代码：

    SELECT a.OrderID, SUM(a.Quantity), c.CompanyName FROM [Order Details] as a 
INNER JOIN Orders as b ON b.OrderID = a.OrderID
INNER JOIN Customers as c ON c.CustomerID = b.CustomerID

GROUP BY a.OrderID

但我无法显示CompanyName。每个订单应该只有一个公司名称，我们不需要连接它。我怎样才能做到这一点？ 我附上我的数据库图表。

Answer 1

您可能遇到的错误是所有非聚合列都应出现在GROUP BY子句中。

所以错误基本上在CompanyName中缺少GROUP BY列。

因此，查询应如下所示：

SELECT
    a.OrderID,
    SUM(a.Quantity) as TotalQuantity,
    c.CompanyName
FROM [Order Details] as a 
INNER JOIN Orders as b ON b.OrderID = a.OrderID
INNER JOIN Customers as c ON c.CustomerID = b.CustomerID
GROUP BY a.OrderID, c.CompanyName

Works