Question

I am tryin to get the min speed value of my records where I have the case the value of the speed is equal 0 in the column speed but I have the case too where the result of my query is 0 because there was no min speed found in the range of 40 meter. How can I distinguish between the both cases?

Code:

    String sql_min_speed = "SELECT mac, stop_name, stop_distance, speed from behaviour "
            + "where stop_distance < 40 and mac = ? and stop_name = ? order by speed LIMIT  1";

    int minSpeed = get_min_speed(macD, con, sql_min_speed, stopName,
            maintain);

get_min_speed method:

private int get_min_speed(String macD, Connection con, String sql,
        String stopName, List<Maintain> maintain) throws SQLException {
    PreparedStatement prepared1 = con.prepareStatement(sql);
    prepared1.setString(1, macD);
    prepared1.setString(2, stopName);
    ResultSet rsBehav1 = prepared1.executeQuery();
    int min_speed = 0;
    while (rsBehav1.next()) {
        String mac = rsBehav1.getString("mac");
        String Stname = rsBehav1.getString("stop_name");
        int distance = rsBehav1.getInt("stop_distance");
        min_speed = rsBehav1.getInt("speed");
        Maintain main1 = new Maintain(mac, Stname, distance, min_speed);
        maintain.add(main1);

    }
    return min_speed;
}

Answer 1

Change int min_speed = 0; to int min_speed = -1;

Then add a condition in caller method.

Answer 2

You can either return a negative value when there's no actual minimum speed to return, or you can change the return type to Integer and return null in that case.

Distinguish between the zero value in the column and as result of the query

2 个答案: