I have a table (user_zip_codes) with the users' zip_code, latitude and longitude. I have found a function here on stackoverflow that finds zip codes within a specific radius:

function zipcodeRadius($lat, $lon, $radius) {
    global $mysqli;
    $zipcodeList = array();
    $radius = ($radius ? $radius : 20);
    $sql = "SELECT userID,city,zip_code,country FROM user_zip_codes  WHERE (3958*3.1415926*sqrt((lat-$lat)*(lat-$lat) + cos(lat/57.29578)*cos($lat/57.29578)*(lon-$lon)*(lon-$lon))/180) <= $radius GROUP BY zip_code";
    if($stmt = $mysqli->prepare($sql)) {
        $stmt->execute();
        $stmt->bind_result($userID,$city,$zip_code,$country);
        while($stmt->fetch()) {
            $zipcodeList[] = array('userID'=>$userID,'city'=>$city,'zip_code'=>$zip_code,'country'=>$country);
        }
    }
    return $zipcodeList;
}

It works perfectly. However, I would like the function to sort the array by distance (either by ASC og DESC). How should I adjust my query in order for this to happen?

Thanks in advance.

UPDATE: The word 'distance' might appear ambiguous (thanks to Jorge). I simply wish to sort the zip_codes by distance meant as the distance between two points.

You could use something like

$iDistance = 20;
$iRadius = 6371; // earth radius in km
$iRadius = 3958; // earth radius in miles
$fLat = x.y; // Your position latitude
$fLon = x.y; // Your position longitude

$strQuery = "
SELECT
  *,
  $iRadius * 2 * ASIN(SQRT(POWER(SIN(( $fLat - abs(pos.lat)) * pi() / 180 / 2),2) +
COS( $fLat * pi()/180) * COS(abs(pos.lat) * pi() / 180) * POWER(SIN(( $fLon - pos.lon) *
pi() / 180 / 2), 2) )) AS distance
FROM user_zip_codes pos
HAVING distance < $iDistance
ORDER BY distance";

where you have to fetch your lat/lon value before using the SQL. This works for me

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