我尝试了几种不同的方式,但是似乎没有插入NULL,下面的一个插入“”,任何人都可以指向正确的方向吗？

这是代码所需的部分,如果你需要更多的只是让我知道.

Dim rdr As sqlDataReader
            Dim cmdInsert As sqlCommand = New sqlCommand()
            cmdInsert.CommandText = "spPersonalDetailsInsert"
            cmdInsert.CommandType = CommandType.StoredProcedure
            cmdInsert.Connection = connsql
 
 
            Dim firstname,lastname,address,address1,town,county,postcode As sqlParameter
            'convert to null if ""
            Dim frmFirstName As String
            If pd_first_name.Text = "" Then
                frmFirstName = Convert.DBNull
            Else
                frmFirstName = pd_first_name.Text
            End If
 
            firstname = New sqlParameter()
            firstname.ParameterName = "@firstname"
            firstname.sqlDbType = sqlDbType.NVarChar
            firstname.Size = 50
            firstname.Direction = ParameterDirection.Input
            firstname.Value = frmFirstName

编辑

我测试了以下代码：

If pd_first_name.Text = "" Then
            frmFirstName = DBNull.Value
        Else
            frmFirstName = pd_first_name.Text
        End If

但是它仍然不会插入NULL,所以我测试了这个：

If pd_first_name.Text = "" Then
                Response.Write("NULL")
                address1.Value = DBNull.Value
            Else
                Response.Write("NOT NULL")
                address1.Value = pd_address1.Text
            End If

所以如果我没有输入到address1字段,它应该将NULL写入屏幕,但它始终写NOT NULL.一个空的表单字段是什么相等的？在经典的ASP它总是“”.