禁止单列输入重复值

假定有个订单表，要求订单号列不能输入重复值，可以将这个表的DataColChanging事件代码设置为：

If e.DataCol.Name = "订单号" Then
    Dim dr As DataRow
    dr = e.DataTable.Find("订单号 = '" & e.NewValue & "'")
    If dr IsNot Nothing Then
        MessageBox.Show("此订单号已经存在!")
        e.Cancel = True
    End If
End If

上述代码设置完成后，不管以任何方式，都无法输入重复的订单号。

Select Case e.DataCol.name
    Case "型号","规格"
        Dim xh As String
        Dim gg As String
        If e.DataCol.Name= "型号" Then
            xh = e.NewValue
            gg = e.DataRow("规格")
        Else
            gg = e.NewValue
            xh = e.DataRow("型号")
        End If
        If xh > "" AndAlso gg  > "" Then
            Dim dr As DataRow = e.DataRow
            If e.DataTable.Find("型号 = '" & xh & "' And 规格 = '" & gg & "'") IsNot Nothing Then
                MessageBox.Show("已经存在相同型号和规格的行!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
                e.Cancel = True
            End If
        End If
End Select

Select Case e.DataCol.name
    Case "型号","规格"
        Dim dr As DataRow = e.DataRow
        If dr.IsNull("型号") = False AndAlso dr.IsNull("规格") = False Then
            If e.DataTable.Compute("Count([_Identify])","型号 = '" & dr("型号") & "' And 规格 = '" & dr("规格") & "'") > 1 Then
                MessageBox.Show("已经存在相同型号和规格的行!","提示",MessageBoxButtons.OK,MessageBoxIcon.Information)
                e.DataRow(e.DataCol.Name) = e.OldValue '取消输入
            End If
        End If
End Select