Question

我想要在整个月份和全年都没有订单的产品列表。

这是我的查询：

SELECT DISTINCT(p.ProductName), 
DATEPART(MM,o.OrderDate),DATEPART(YY,o.OrderDate) 
FROM Products p 
JOIN [Order Details] od on p.ProductID = od.ProductID
JOIN Orders o on o.OrderID = od.OrderID
GROUP BY (p.ProductName), DATEPART(MM,o.OrderDate),DATEPART(YY,o.OrderDate)

Answer 1

使用define: in definition of dotproduct, found bad argument a -- an error. To debug this try: debugmode(true);：

not exists

select p.* from products p where not exists (select 1 from Orders o join [Order Details] od on o.OrderID = od.OrderID where p.ProductID = od.ProductID and year(o.orderdate) = ? );用于利息年度。

Answer 2

我在下面的代码中使用类来模拟您的数据库。看看此代码是否有效

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            List<Product> Products = new List<Product>();
            List<Order> Orders = new List<Order>();

            var results = (from o in Orders
                          join p in Products on o.ProductID equals p.ProductID
                          select new {order = o, name = p.ProductName})
                          .OrderByDescending(x => x.order.OrderDate)
                          .GroupBy(x => x.order.ProductID)
                          .Select(x => x.FirstOrDefault()) //get last order for each product
                          .Where(x => x.order.OrderDate < DateTime.Now.AddMonths(-6))
                          .Select(x => new { Name = x.name, ID = x.order.ProductID, Date = x.order.OrderDate})
                          .ToList();
        }
    }
    public class Product
    {
        public string ProductName { get; set; }
        public string ProductID { get; set; }
    }
    public class Order
    {
        public DateTime OrderDate { get; set; }
        public string ProductID { get; set; }
    }
}

此代码效率更高，因为它不必加入不需要的项目

            var results = Orders.OrderByDescending(x => x.OrderDate)
                          .GroupBy(x => x.ProductID)
                          .Select(x => x.FirstOrDefault()) //get last order for each product
                          .Where(x => x.OrderDate < DateTime.Now.AddMonths(-6))
                          .Select(x => new { Name = Products.Where(y => y.ProductID == x.ProductID).FirstOrDefault().ProductName , ID = x.ProductID, Date = x.OrderDate })
                          .ToList();

如果没有用于产品的订单

            var resultsx = (from o in Orders
                           join p in Products on o.ProductID equals p.ProductID into ps 
                           from p in ps.DefaultIfEmpty() 
                           select new { order = o, name = p.ProductName })
                           .OrderByDescending(x => x.order == null ? new DateTime() : x.order.OrderDate)
                          .GroupBy(x => x.order.ProductID)
                          .Select(x => x.FirstOrDefault()) //get last order for each product
                          .Where(x => x.order == null ? true : x.order.OrderDate < DateTime.Now.AddMonths(-6))
                          .Select(x => new { Name = x.name, ID = x.order == null ? "" : x.order.ProductID, Date = x.order == null ? new DateTime() : x.order.OrderDate })
                          .ToList();

获取所有月份和年份中没有任何订单的产品列表

2 个答案: