Calculate Distance between 2 Geo Locations in PHP MySQL

Geolocation serves in a multitude of contexts. In this internet era, everything is on the single palm. Various technology uses various methods to get geolocations and distance between two locations.
We are going to use PHP MySQL as technology to calculate the distance between two geo coordinates.

How can I do that?

Using MySQL Query

So, I have a table geo_cord containing two fields latitude and longitude and I need to calculate the user input distance in km with another user inputs user_latitude and user_longitude.

Well! we need to write a query:

We need to find all results from Database within user input distance

$distance = 50; // user input distance
$user_latitude = '26.826999'; // user input latitude
$user_longitude = '-158.265114'; // user input logtitude

$sql = "SELECT ROUND(6371 * acos (cos ( radians($user_latitude) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians($user_longitude) ) + sin ( radians($user_latitude) ) * sin( radians( latitude ) ))) AS distance,geo_cord.* FROM geo_cord HAVING distance <= $distance";

To convert to miles, multiply by 3971.
To convert to kilometers, multiply by 6373.
To convert to meters, multiply by 6373000.
To convert to feet, multiply by (3971 * 5280) 20914080.

There are other methods to achieve the same result, but I prefer this simple method with less coding and quick result.

Using PHP

I have found a formula in Wikipedia Haversine formula which determines the great-circle distance between two points on a sphere given their longitudes and latitudes.

So it also gives result:

function distance($latitude1, $longitude1, $latitude2, $longitude2) { 
        $pi80 = M_PI / 180; 
        $lat1 *= $pi80; 
        $lon1 *= $pi80; 
        $lat2 *= $pi80; 
        $lon2 *= $pi80; 
        $r = 6372.797; // radius of Earth in km 6371
        $dlat = $lat2 - $lat1; 
        $dlon = $lon2 - $lon1; 
        $a = sin($dlat / 2) * sin($dlat / 2) + cos($lat1) * cos($lat2) * sin($dlon / 2) * sin($dlon / 2); 
        $c = 2 * atan2(sqrt($a), sqrt(1 - $a)); 
        $km = $r * $c; 
        return round($km); 
    }