Vb.net 数据表。使用和条件选择不'；我不能给出预期的结果

我正在尝试比较两个数据表，并使用

DataTable进行一些测试。在两个相同的数据表上选择
：

Using DT_NewData As DataTable = DT_DBData.Copy
    For x As Short = 0 To DT_NewData.Rows.Count - 1
        Dim SelRows As DataRow() = DT_DBData.Select( _
            "Type='" & DT_NewData.Rows(x)("Type") & "'" & _
            " AND In_Date='" & DT_NewData.Rows(x)("In_Date") & "'" & _
            " AND Out_Date='" & DT_NewData.Rows(x)("Out_Date") & "'")
    Next

但是
SelRows.Length
始终为0。我的代码出了什么问题？
尽管该表的副本有点奇怪，但请尝试以下操作：

假设
Type
是
String

Imports Microsoft.VisualBasic
Imports System.Linq

Module StartupModule

Sub Main()
    ' Declare the table.
    Dim originalDataTable As New DataTable

    ' Declare the table columns.
    With originalDataTable.Columns
        .Add("Type", GetType(String))
        .Add("InDate", GetType(DateTime))
        .Add("OutDate", GetType(DateTime))
    End With

    ' Delegate to add rows.
    Dim addRow As Action(Of String, DateTime?, DateTime?) = Sub(text, inDate, outDate)
    Dim newRow As DataRow = originalDataTable.NewRow()

    With newRow
        If (Not String.IsNullOrEmpty(text)) Then
            .SetField(Of String)("Type", text)
        End If

        If (inDate.HasValue) Then
            .SetField(Of DateTime?)("InDate", inDate.Value)
        End If

        If (outDate.HasValue) Then
            .SetField(Of DateTime?)("OutDate", outDate.Value)
        End If
    End With

    originalDataTable.Rows.Add (newRow)
End Sub

' Adding rows to the table.
addRow("type1", #2/2/2017#, Nothing)
addRow(Nothing, #1/25/2016#, Nothing)
addRow(Nothing, Nothing, #1/30/2016#)

' Copy the table
Dim copiedDataTable As DataTable = originalDataTable.Copy

' Loop through copied table rows.
For i As Integer = 0 To copiedDataTable.Rows.Count - 1
    Dim type As String = copiedDataTable.Rows(i).Field(Of String)("Type")
    Dim inDate As DateTime? = copiedDataTable.Rows(i).Field(Of DateTime?)("InDate")
    Dim outDate As DateTime? = copiedDataTable.Rows(i).Field(Of DateTime?)("OutDate")

    ' Using DataTable Select.
    Dim filter As String = String.Format("{0} {1} {2}",
        If(type Is Nothing, "( Type Is Null )", String.Format("( Type = '{0}' )", type)),
        If(Not inDate.HasValue, "And ( InDate Is Null )", String.Format("And ( InDate = '{0}' )", inDate.Value.ToString())),
        If(Not outDate.HasValue, "And ( OutDate Is Null )", String.Format("And ( OutDate = '{0}' )", outDate.Value.ToString())))

    Dim usingSelectRows As DataRow() = originalDataTable.Select(filter)
    Console.WriteLine("usingSelectRows.Count = {0}", usingSelectRows.Count)

    ' Using Linq.
    Dim typeSelector As Func(Of DataRow, Boolean) = Function(r)
    If (IsNothing(type)) Then
        Return IsNothing(r.Field(Of String)("Type"))
    Else
        Return r.Field(Of String)("Type") = type
    End If
End Function

    Dim inDateSelector As Func(Of DataRow, Boolean) = Function(r)
    If (Not inDate.HasValue) Then
        Return Not r.Field(Of DateTime?)("InDate").HasValue
    Else
        Return r.Field(Of DateTime?)("InDate").GetValueOrDefault.CompareTo(inDate.GetValueOrDefault) = 0
    End If
End Function

    Dim outDateSelector As Func(Of DataRow, Boolean) = Function(r)
    If (Not outDate.HasValue) Then
        Return Not r.Field(Of DateTime?)("OutDate").HasValue
    Else
        Return r.Field(Of DateTime?)("OutDate").GetValueOrDefault.CompareTo(outDate.GetValueOrDefault) = 0
    End If
End Function

    Dim usingLinqRows = From r In originalDataTable.AsEnumerable
                Where
                    (typeSelector(r)) AndAlso
                    (inDateSelector(r)) AndAlso
                    (outDateSelector(r))
                Select r

    Console.WriteLine("usingLinqRows.Count = {0}", usingLinqRows.Count)

    Console.WriteLine()
Next

    Console.ReadLine()
End Sub

End Module

始终使用扩展名
DataRow
来检索数据。
您应该使用
选项Strict On
，这样它就不会编译。您不能仅使用字符串将对象与
&
合并。我假设
In\u Date
和
Out\u Date
是日期列。关闭选项Strict后，通过使用
ToString
将其自动转换为字符串。这不会返回数据表所需的日期的固定区域性格式。请选择当前区域性的格式。所以使用
DT_NewData.Rows（x）.Field（Of Date）（“In_Date”）.ToString（CultureInfo.InvariantCulture）
@TimSchmelter Ok。我理解我的错误。无论如何，当字段为
DBNull
时，您的建议将返回
无效强制转换异常。你能建议另一种方法吗？你试过了吗？是否也使用
DBNull
数据字段？在我的场景
SelRows中，长度
为0。@genespos我已经用一个完整的例子编辑了我的答案。谢谢你的努力，但我不是专家，我正在尝试通过比较每个单元格（排序后）来解决问题。没问题，我的朋友。问题从数据表中的空值开始。希望我的例子有帮助。