Question

我正在使用northwind紧凑版数据库，而我正在尝试提取哪些销售人员赚了多少钱。

因此，我的查询的内部部分工作正常，因为我得到了一个包含总费用的员工ID列表：

select orderCosts."Employee ID", sum(orderCosts.Cost) as OrderCost from
   (
       select Orders."Order Id",orders."Employee ID", orders."Customer ID", "Order Details"."Unit Price" * "Order Details"."Quantity" as Cost from orders
       inner join "Order Details"
       On Orders."Order ID" = "Order Details"."Order ID"
   ) orderCosts
   group by ordercosts."Employee ID"

我认为没问题，然后我会尝试将其加入到员工表中，这似乎并不复杂，但现在我收到"The table aliases must be unique. [Name of duplicate alias = employeePerformance]"错误。我像以前一样嵌入并命名了表格，如下所示：

select Employees."FirstName", Employees."LastName", employeePerformance.OrderCost
from
(
   select orderCosts."Employee ID", sum(orderCosts.Cost) as OrderCost from
   (
       select Orders."Order Id",orders."Employee ID", orders."Customer ID", "Order Details"."Unit Price" * "Order Details"."Quantity" as Cost from orders
       inner join "Order Details"
       On Orders."Order ID" = "Order Details"."Order ID"
   ) orderCosts
   group by ordercosts."Employee ID"
) employeePerformance
inner join employeePerformance
On Emplyees."Employee ID" = employeePerformance."Employee ID"

我可以看到，我只是宣布一次empployeePerformance，然后试图加入它，所以为什么它认为我已经两次了？

我对SQL很陌生，所以如果我正在做一些愚蠢的事情，请善待！

Answer 1

我认为你应该在员工上添加一个FROM，在子查询上添加一个连接（如果我理解的话）

select Employees."FirstName", Employees."LastName", employeePerformance.OrderCost
from Employees
INNER JOIN
(
   select orderCosts."Employee ID", sum(orderCosts.Cost) as OrderCost from
   (
       select Orders."Order Id",orders."Employee ID", orders."Customer ID", "Order Details"."Unit Price" * "Order Details"."Quantity" as Cost from orders
       inner join "Order Details"
       On Orders."Order ID" = "Order Details"."Order ID"
   ) orderCosts
   group by ordercosts."Employee ID"
) employeePerformance

On Employees."Employee ID" = employeePerformance."Employee ID"

因为在您的查询中，您在employeesperformance =＆gt;上对employeesPerformance和inner join进行了FROM重复的名称，这是不允许的。

顺便说一下，我认为你的查询可以大大简化：

SELECT e."FirstName", e."LastName", sum(od."Unit Price" * od."Quantity") as OrderCosts
FROM employees e
inner join orders o on o."Employee ID" = e."Employee ID"
inner join "Order Details" od on od."Order ID" = o."Order ID"
group by e."Employee ID", e."FirstName", e."LastName"

如果您希望员工没有订单/订单明细，请使用左连接而不是内连接（并在单价和数量上合并）。

SELECT e."FirstName", e."LastName", sum(coalesce(od."Unit Price", 0) * coalesce(od."Quantity", 0)) as OrderCosts
FROM employees e
left join orders o on o."Employee ID" = e."Employee ID"
left join "Order Details" od on od."Order ID" = o."Order ID"
group by e."Employee ID", e."FirstName", e."LastName"

无法内部连接到嵌入式查询

1 个答案: