Linq to sql 具有多个联接、分组方式和计数的LINQ到SQL
我有3个表,Cust、Order和Item,其中包含以下相关字段:Linq to sql 具有多个联接、分组方式和计数的LINQ到SQL,linq-to-sql,Linq To Sql,我有3个表,Cust、Order和Item,其中包含以下相关字段: Cust - CustID, CustName Order - OrderID, CustID Item - ItemID, OrderID 我想找到每个客户的订单和商品总数 下面是一个SQL语句,它生成我想要的,一个客户列表,其中包含每个客户的订单总数和订购的项目总数 SELECT Cust.CustID, Cust.CustName, count(DISTINCT Order.OrderID) AS numOrde
Cust - CustID, CustName
Order - OrderID, CustID
Item - ItemID, OrderID
我想找到每个客户的订单和商品总数
下面是一个SQL语句,它生成我想要的,一个客户列表,其中包含每个客户的订单总数和订购的项目总数
SELECT
Cust.CustID, Cust.CustName,
count(DISTINCT Order.OrderID) AS numOrders,
count(DISTINCT Item.ItemID ) AS numItems
FROM Cust
LEFT JOIN Order ON Order.CustID = Cust.CustID
LEFT JOIN Item ON Item.OrderID = Order.OrderID
GROUP BY Cust.CustID, Cust.CustName
ORDER BY numItems
我将其转换为LINQ的第一次尝试是仅计算项目,并得出以下结论:
var qry = from Cust in tblCust
join Order in tblOrder on Cust.CustID equals Order.CustID
join Item in tblItem on Order.OrderID equals Item.OrderID
group Cust by new {CustID = Cust.CustID, CustName = Cust.CustName} into grp
orderby grp.Count()
select new
{
ID = grp.Key.CustID,
Name = grp.Key.CustName,
Cnt = grp.Count()
};
使用此代码,我得到了一个异常:
Value cannot be null. Parameter name: inner
我走对了吗?我要怎么做才能得到两个计数
from
和where
以及DefaultIfEmpty
var qry =
from Cust in tblCust
from Order in tblOrder.Where(x => Cust.CustID == x.CustID)
.DefaultIfEmpty()
from Item in tblItem.Where(x => Order.OrderID == x.OrderID)
.DefaultIfEmpty()
group new { Cust, Order.OrderId, Item.ItemId } by new { Cust.CustID, Cust.CustName } into grp
let numItems = grp.Select(x => x.ItemId).Distinct().Count()
orderby numItems
select new
{
ID = grp.Key.CustID,
Name = grp.Key.CustName,
numOrders = grp.Select(x => x.OrderId).Distinct().Count(),
numItems,
};
但有一个问题,“orderby grp.Count()”与“numems”有什么关系?