สอบถามการเขียนโปรแกรมบันทึกเวลาเข้า-ออกครับ vb.net+sql

Private Sub btnIN_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnIN.Click
        Dim dt As String
        dt = DateTime.Now.ToString("dd-MM-yyyy HH:mm:ss")
        Dim strSQL As String
        Dim intNumRows As Integer
        sqlcon = New SqlConnection("Server=TOSHIBA-PC\SQLEXPRESS;Database=parking;Trusted_Connection=True;")
        sqlcon.Open()
        strSQL = "SELECT COUNT(*) FROM member WHERE CardSN = '" & txtSN2.Text & "'"
        sqlcmd = New SqlCommand(strSQL, sqlcon)
        intNumRows = sqlcmd.ExecuteScalar()
        If intNumRows > 0 Then
            ds = New DataSet
            da = New SqlDataAdapter("INSERT INTO inout (CardSN,dtin) VALUES ('" & txtSN2.Text & "','" & dt & "');", sqlcon)      'บันทึกเวลาเมื่อกดปุ่ม เข้า
            da.Fill(ds, "inout")
            Call showdata2()
        Else
            MessageBox.Show("คุณไม่ได้เป็นสมาชิก")
        End If
        sqlcon.Close()
    End Sub

Private Sub btnOUT_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOUT.Click
        Dim dt As String
        dt = DateTime.Now.ToString("dd-MM-yyyy HH:mm:ss")
        ds = New DataSet
        da = New SqlDataAdapter("ALTER TABLE inout ADD CONSTRAINT chk_Time CHECK (CardSN='" & txtSN2.Text & "' AND dtout='')", sqlcon)
        da = New SqlDataAdapter("UPDATE inout SET dtout='" & dt & "'WHERE CardSN='" & txtSN2.Text & "'", sqlcon)
        da.Fill(ds, "inout")
        Call showdata2()
    End Sub