VB.net 提供了通过Linq对数据集进行合计非常方法，可以减少了与数据库的交互，提高系统性能，以下是sum示示例：
1、对字典对象的sum
dis.Sum(Function(a) a.Value) 'dis是Dictionary
当然也可以用
Mytb.Compute("Sum(USM_TOTAL_CASH_MONEY)","")
2、对datatable的单字段sum
(From row In tmptable Select row.Field(Of Decimal)("customer_ds")).Sum() 'tmptable是DataTable对象,customer_ds是合计字段
3、对DataTable的多字段sum
Dim sumtable2 = From r In MyTb
Group r By Key = New With {Key .Key = "合计"} Into g = Group
Select New With {.key = Key,.totalMoney = g.Sum(Function(x) IIf(IsDBNull(x("A1")),x("A1"))),.saleMoney = g.Sum(Function(x) IIf(IsDBNull(x("A2")),x("A2"))),.CaSh = g.Sum(Function(x) IIf(IsDBNull(x("A3")),x("A3"))),.CardPay = g.Sum(Function(x) IIf(IsDBNull(x("A4")),x("A4"))),.OtherPay = g.Sum(Function(x) IIf(IsDBNull(x("A5")),x("A5"))),.CkPay = g.Sum(Function(x) IIf(IsDBNull(x("A6")),x("A6"))),.DyqPay = g.Sum(Function(x) IIf(IsDBNull(x("A7")),x("A7"))),.Minus = g.Sum(Function(x) IIf(IsDBNull(x("A8")),x("A8"))),.orders = g.Sum(Function(x) IIf(IsDBNull(x("A9")),x("A9"))),.newCards = g.Sum(Function(x) IIf(IsDBNull(x("A10").ToString().Split("/")(0)),x("A11").ToString().Split("/")(0))) & "/" &
g.Sum(Function(x) IIf(IsDBNull(x("A11").ToString().Split("/")(1)),x("A11).ToString().Split("/")(1))),.cardInNums = g.Sum(Function(x) IIf(IsDBNull(x("充卡张数/金额").ToString().Split("/")(0)),x("充卡张数/金额").ToString().Split("/")(0))) & "/" &
g.Sum(Function(x) IIf(IsDBNull(x("充卡张数/金额").ToString().Split("/")(1)),x("充卡张数/金额").ToString().Split("/")(1)))
}
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