public static DataSet getOrdersDataSet(string dateStart, string dateEnd)
    {
        SqlConnection conn = Utils.getSQLConnection();

        SqlCommand cmd = new SqlCommand();

        cmd.CommandText = "SELECT orders.oid, orders.orddate, itemsPerOrder.itemsCount FROM orders, (";
        cmd.CommandText += "SELECT oid, count(*) itemsCount FROM items GROUP BY oid";
        cmd.CommandText += ") itemsPerOrder WHERE orders.oid = itemsPerOrder.oid";

        if (dateStart != null && dateStart.Length > 0)
            cmd.CommandText += " AND DATEDIFF(day,'"+dateStart+"',orddate) >= 0";

        if (dateEnd != null && dateEnd.Length > 0)
            cmd.CommandText += " AND DATEDIFF(day,'"+dateEnd+"',orddate) <= 0";

        cmd.Connection = conn;

        SqlDataAdapter sda = new SqlDataAdapter();

        DataSet ds = new DataSet();

        sda.SelectCommand = cmd;

        conn.Open();

        sda.Fill(ds);

        conn.Close();

        return ds;
    }