Linq实战

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

(Function(a) ) 'dis是Dictionary

当然也可以用 

("Sum(USM_TOTAL_CASH_MONEY)", "")

2、对datatable的单字段sum

(From row In tmptable Select (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 = (Function(x) IIf(IsDBNull(x("A1")), 0, x("A1"))),
                               .saleMoney = (Function(x) IIf(IsDBNull(x("A2")), 0, x("A2"))),
                               .CaSh = (Function(x) IIf(IsDBNull(x("A3")), 0, x("A3"))),
                               .CardPay = (Function(x) IIf(IsDBNull(x("A4")), 0, x("A4"))),
                               .OtherPay = (Function(x) IIf(IsDBNull(x("A5")), 0, x("A5"))),
                               .CkPay = (Function(x) IIf(IsDBNull(x("A6")), 0, x("A6"))),
                               .DyqPay = (Function(x) IIf(IsDBNull(x("A7")), 0, x("A7"))),
                               .Minus = (Function(x) IIf(IsDBNull(x("A8")), 0, x("A8"))),
                               .orders = (Function(x) IIf(IsDBNull(x("A9")), 0, x("A9"))),
                               .newCards = (Function(x) IIf(IsDBNull(x("A10").ToString().Split("/")(0)), 0, x("A11").ToString().Split("/")(0))) & "/" &
                                           (Function(x) IIf(IsDBNull(x("A11").ToString().Split("/")(1)), 0, x("A11).ToString().Split("/")(1))),
        .cardInNums = (Function(x) IIf(IsDBNull(x("充卡张数/金额").ToString().Split("/")(0)), 0, x("充卡张数/金额").ToString().Split("/")(0))) & "/" &
                     (Function(x) IIf(IsDBNull(x("充卡张数/金额").ToString().Split("/")(1)), 0, x("充卡张数/金额").ToString().Split("/")(1)))
                              }