I want to update a column of a table where the column name will be entered in the textbox while executing. The following code is not performing any action. TextBox14 contains the column name and...

Dim squery As String = "SELECT name,days from definedLeave"
                        Dim cmd6 As SqlCommand = New SqlCommand(squery, con)
                        Dim dr6 As SqlDataReader = cmd6.ExecuteReader()
                        Dim i As Integer = 0
                        While dr6.Read()
                            Try
                                s = dr6(i).ToString
                                TextBox14.Text = s
                                a = dr6(i + 1).ToString
                                TextBox12.Text = a
                               Dim sql = "update empLeave set " & TextBox14.Text.Trim & "=@na where epid='" + txtCode.Text + "'"

                                Using com7 = New SqlCommand(sql, con)
                                    com7.Parameters.AddWithValue("@na", TextBox12.Text)
                                    com7.ExecuteNonQuery()
                                End Using
                            Catch ex As Exception
        MsgBox("HELLO")
    End Try
                        End While
                        com7.Dispose()
                        dr6.Close()