来源:https://codedefault.com/2018/group-by-multiple-columns-and-sum-in-csharp
.NET[C#]LINQ按多列分组(Group By)并计算总和(Sum) SQL语句: SELECT * FROM <TableName> GROUP BY <Column1>,<Column2> QuantityBreakdown ( MaterialID int, ProductID int, Quantity float ) INSERT INTO @QuantityBreakdown (MaterialID, ProductID, Quantity) SELECT MaterialID, ProductID, SUM(Quantity) FROM @Transactions GROUP BY MaterialID, ProductID 在C#中,如何使用LINQ实现以上SQL语句中的需求呢?方式归纳如下: 方式一 var query = (from t in Transactions group t by new {t.MaterialID, t.ProductID} into grp select new { grp.Key.MaterialID, grp.Key.ProductID, Quantity = grp.Sum(t => t.Quantity) }).ToList(); 方式二 from grouping in list.GroupBy(x => new Tuple<string,string,string>(x.Person.LastName,x.Person.FirstName,x.Person.MiddleName)) select new SummaryItem { LastName = grouping.Key.Item1, FirstName = grouping.Key.Item2, MiddleName = grouping.Key.Item3, DayCount = grouping.Count(), AmountBilled = grouping.Sum(x => x.Rate), } 方式三 var Results= query.GroupBy(x => new { x.Column1, x.Column2 });
易错提醒:
grp.Key.ProductID, //前往不要忘了Key!!!
Quantity = grp.Sum(t => t.Quantity) //必须取别名Quantity !!!