protected void CamFactura()
{
    DataTable dtr = new DataTable();
    OdbcCommand cm = new OdbcCommand("SELECT SlpCode FROM Vendedores WHERE SlpName = '" + Request.QueryString["id"] + "'", cn);
    OdbcDataAdapter da = new OdbcDataAdapter(cm);
    da.Fill(dtr);
    cn.Open();
    DataRow fila1 = dtr.Rows[0];
    if (dtr.Rows.Count == 1)
    {

        DataTable dt2 = new DataTable();
        OdbcCommand cmd2 = new OdbcCommand("SELECT count(noFactura) FROM SVenta WHERE SlpCode = '" + Convert.ToString(fila1["SlpCode"]) + "'", cn);
        int count = Convert.ToInt32(cmd2.ExecuteScalar());
        if(count == 0)
        {
            label2.Text = "1";
        }
        else
        {
            OdbcCommand cmd4 = new OdbcCommand("SELECT (max(noFactura) +1) FROM SVenta WHERE SlpCode ='" + Convert.ToString(fila1["SlpCode"]) + "'", cn);
            label2.Text = Convert.ToString(cmd4.ExecuteScalar());
        }
    }
    cn.Close();
}