select by range/distance geo/latitude/longitude

function.php

<?php
public static function distance($lat1, $lon1, $lat2, $lon2, $unit) { 
  $theta = $lon1 - $lon2; 
  $dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) +  cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta)); 
  $dist = acos($dist); 
  $dist = rad2deg($dist); 
  $miles = $dist * 60 * 1.1515;
  $unit = strtoupper($unit);

  if ($unit == "K") {
    return ($miles * 1.609344); 
  } else if ($unit == "N") {
    return ($miles * 0.8684);
  } else {
    return $miles;
  }
}

sql.php

<?php
$range = 10; // km
$precision = 2; // 10.13km
$lat = 12.123456; // punto di partenza
$lng = 34.123456; // punto di partenza

$sql = "
select
 *,
 round(( 6371 * acos( cos( radians(".addslashes($lat).") ) * cos( radians( d.distributore_latitudine ) ) * cos( radians( d.distributore_longitudine ) - radians(".addslashes($lng).") ) + sin( radians(".addslashes($lat).") ) * sin( radians( d.distributore_latitudine ) ) ) ), ".$precision.") as distance   
from luogo
where attivo = 1
and latitudine != '0'
and longitudine != '0'
having distance <= '".addslashes($range)."'
and distance != 0
order by distance asc";