sql 使用 northwind 数据库查询到 c#
sql query to c# using northwind DB
使用 northwind 数据库,我必须进行查询以获取员工姓名、每位员工的订单量以及这些订单的平均价格
这是 SQL
中的查询
SELECT TOP 10
a.LastName, a.FirstName, amountOfOrders = COUNT(DISTINCT b.OrderID), AveragePricePerOrder = SUM(c.Quantity*c.UnitPrice) /COUNT(DISTINCT b.OrderID)
FROM Employees a join orders b on (a.EmployeeID = b.EmployeeID)
join [Order Details] c on b.OrderID = c.OrderID
Group BY a.EmployeeID, a.LastName, a.FirstName
ORDER BY amountOfOrders Desc
这运行良好,但我必须在 C# 中实现,但我有点卡住了
到目前为止,我得到了这个
var query_rx = (from c in ctx.Employees
join or in ctx.Orders on c.EmployeeID equals or.EmployeeID
join ord in ctx.Order_Details on or.OrderID equals ord.OrderID
group c by new
{
c.EmployeeID,
c.LastName,
c.FirstName,
amount = c.Orders.Count
} into c
orderby c.Key.amount descending
select new
{
c.Key.LastName,
c.Key.FirstName,
amountOfOrders = c.Key.amount
}).Take(10);
"edit" 我在计算平均值时遇到问题,尝试了很多方法但我无法让它工作
"edit" 在 Dohnal 的建议的帮助下,我对查询做了一些更改。
这看起来几乎完全像我想要的列, 除了 字段 lastname 和 firstname 是 blank,即使使用 ToString
var query_rx = (from or in ctx.Order_Details
join ord in ctx.Orders on or.OrderID equals ord.OrderID
group or by new
{
ord.EmployeeID
} into c
orderby c.Select(x => x.OrderID).Distinct().Count() descending
select new
{
Lastname = (from emp in ctx.Employees
where c.Key.EmployeeID == emp.EmployeeID
select emp.LastName),
Firstname = (from emp in ctx.Employees
where c.Key.EmployeeID == emp.EmployeeID
select emp.FirstName),
c.Key.EmployeeID,
AmountOfOrders = c.Select(x => x.OrderID).Distinct().Count(),
AveragePricePerOrder = c.Sum(x => x.Quantity * x.UnitPrice) / c.Select(x => x.OrderID).Distinct().Count()
}).Take(10);
试试这个查询:
var query = (from emp in ctx.Employers
join order in ctx.Orders on emp.EmployeeID equals order.EmployerID
join orderDet in ctx.Order_Details on order.OrderID equals orderDet.OrderID
group new { emp, order, orderDet }
by new { emp.FirstName, emp.LastName, emp.EmployeeID, order.OrderID }
into orderGroup
let a = new
{
orderGroup.Key.EmployeeID,
orderGroup.Key.FirstName,
orderGroup.Key.LastName,
orderGroup.Key.OrderID,
sum1 = orderGroup.Sum(x => x.orderDet.Quantity * x.orderDet.UnitPrice),
}
group a by new { a.FirstName, a.LastName, a.EmployeeID } into empGroup
let a2 = new
{
empGroup.Key.FirstName,
empGroup.Key.LastName,
sum = empGroup.Sum(x => x.sum1),
count = empGroup.Count()
}
orderby a2.count descending
select new
{
a2.FirstName,
a2.LastName,
amountOfOrders = a2.count,
AveragePricePerOrder = a2.sum / a2.count
}).Take(10);
使用 northwind 数据库,我必须进行查询以获取员工姓名、每位员工的订单量以及这些订单的平均价格
这是 SQL
中的查询SELECT TOP 10
a.LastName, a.FirstName, amountOfOrders = COUNT(DISTINCT b.OrderID), AveragePricePerOrder = SUM(c.Quantity*c.UnitPrice) /COUNT(DISTINCT b.OrderID)
FROM Employees a join orders b on (a.EmployeeID = b.EmployeeID)
join [Order Details] c on b.OrderID = c.OrderID
Group BY a.EmployeeID, a.LastName, a.FirstName
ORDER BY amountOfOrders Desc
这运行良好,但我必须在 C# 中实现,但我有点卡住了
到目前为止,我得到了这个
var query_rx = (from c in ctx.Employees
join or in ctx.Orders on c.EmployeeID equals or.EmployeeID
join ord in ctx.Order_Details on or.OrderID equals ord.OrderID
group c by new
{
c.EmployeeID,
c.LastName,
c.FirstName,
amount = c.Orders.Count
} into c
orderby c.Key.amount descending
select new
{
c.Key.LastName,
c.Key.FirstName,
amountOfOrders = c.Key.amount
}).Take(10);
"edit" 我在计算平均值时遇到问题,尝试了很多方法但我无法让它工作
"edit" 在 Dohnal 的建议的帮助下,我对查询做了一些更改。 这看起来几乎完全像我想要的列, 除了 字段 lastname 和 firstname 是 blank,即使使用 ToString
var query_rx = (from or in ctx.Order_Details
join ord in ctx.Orders on or.OrderID equals ord.OrderID
group or by new
{
ord.EmployeeID
} into c
orderby c.Select(x => x.OrderID).Distinct().Count() descending
select new
{
Lastname = (from emp in ctx.Employees
where c.Key.EmployeeID == emp.EmployeeID
select emp.LastName),
Firstname = (from emp in ctx.Employees
where c.Key.EmployeeID == emp.EmployeeID
select emp.FirstName),
c.Key.EmployeeID,
AmountOfOrders = c.Select(x => x.OrderID).Distinct().Count(),
AveragePricePerOrder = c.Sum(x => x.Quantity * x.UnitPrice) / c.Select(x => x.OrderID).Distinct().Count()
}).Take(10);
试试这个查询:
var query = (from emp in ctx.Employers
join order in ctx.Orders on emp.EmployeeID equals order.EmployerID
join orderDet in ctx.Order_Details on order.OrderID equals orderDet.OrderID
group new { emp, order, orderDet }
by new { emp.FirstName, emp.LastName, emp.EmployeeID, order.OrderID }
into orderGroup
let a = new
{
orderGroup.Key.EmployeeID,
orderGroup.Key.FirstName,
orderGroup.Key.LastName,
orderGroup.Key.OrderID,
sum1 = orderGroup.Sum(x => x.orderDet.Quantity * x.orderDet.UnitPrice),
}
group a by new { a.FirstName, a.LastName, a.EmployeeID } into empGroup
let a2 = new
{
empGroup.Key.FirstName,
empGroup.Key.LastName,
sum = empGroup.Sum(x => x.sum1),
count = empGroup.Count()
}
orderby a2.count descending
select new
{
a2.FirstName,
a2.LastName,
amountOfOrders = a2.count,
AveragePricePerOrder = a2.sum / a2.count
}).Take(10);