主题：关于Compute的问题

一个查询窗口中有个“导入选定”按钮，代码如下：

Dim tbl As Table = Tables("ERP订单查询_Table1")
Dim db As String=tbl.DataTable.name
For Each dr1 As DataRow In DataTables("授权表").Select("用户名 = '" & Vars("_UserName") & "'" )
    If dr1("表名") =Tables(MainTable.Name).Name AndAlso dr1("不可增加")=False Then
        For Each r1 As Row In Tables("ERP订单查询_Table1").GetCheckedRows
            If  DataTables(MainTable.Name).Find("交货期 = #" & r1("确定交期") & "# and 订单号 = '" & r1("订单号") & "' and 成品类别 = '" & r1("料品类别") & "'and 成品名称 = '" & r1("料品名称") & "'") Is Nothing Then
                Dim r2 As Row  = Tables(MainTable.Name).AddNew()
                r2("交货期") = r1("确定交期")
                r2("订单号") = r1("订单号")
                r2("成品类别") = r1("料品类别")
                r2("成品名称") = r1("料品名称")
                Dim Sum As Double
                Sum = tbl.Compute("Sum(打数)", "[订单号] = '" & r1("订单号") & "'and [确定交期] = #" & r1("确定交期") & "# And [料品类别] = '" & r1("料品类别") & "' and [料品名称] = '" & r1("料品名称") & "'")
                r2("打数") = sum
            End If
           
        Next
    End If
Next

执行后得到的数据中的“打数”列有些对有些为0，真的想不明白啊！