Question

为了简化这篇文章，假设我在Orders表中有如下数据。这里CustomerId是Customers表的外键。问题：我们如何编写LINQ查询来查找每个客户订购的蔬菜（V）和水果（F）的数量？

订单表：

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我可以按如下方式计算每个客户的订单数量。 OrderId | CustomerId | OrderType 1 | 11 | V 2 | 11 | V 3 | 11 | F 4 | 11 | V 5 | 12 | V 6 | 15 | F 7 | 15 | V 8 | 15 | F：

But how about number of Vegetables and number of Fruits in each order?

Answer 1

您可以使用子查询：

var Query1 = from o in Orders
             group o by o.CustomerId into grp
             select new {
                 CustomerId = grp.Key,
                 OrderCount = grp.Count(),
                 OrderCounts = from g in grp
                               group g by g.OrderType into grp2
                               select new { OrderType = grp2.Key, Count = grp2.Count() }
             };

或者您可以按CustomerId和OrderType进行分组：

var Query1 = from o in Orders
             group o by new { o.CustomerId, o.OrderType } into grp
             select new {
                 CustomerId = grp.Key.CustomerId,
                 OrderType = grp.Key.OrderType,
                 OrderCount = grp.Count()
             };

他们都将返回相同的数据，但形式略有不同。

LINQ to SQL - 计算每个订单中某些项类型的数量

1 个答案: