MySQL query to find zip-codes within given radius from any point (or zip-code)

MySQL_zipcodes_within_radius.sql

/* Given table 'zipcodes' with columns: 
   zipcode, latitude, longitude.
   Find zipcodes within radius from given zipcode.
   EXAMPLE:
   Coordinates for zip 91326 and radius 25 mi: 
*/
SET @location_lat = 34.2766, 
    @location_lon = -118.544; 

SELECT zipcode, ( 3959 * acos( cos( radians(@location_lat) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians(@location_lon) ) + sin( radians(@location_lat) ) * sin( radians( latitude ) ) ) ) AS distance
FROM zipcodes
HAVING distance < 25;

/*
	Result:
	+-------------+-------------------+
	| zipcode     | distance          |
	+-------------+-------------------+
	| 90004       | 19.32764527143567 |
	| 90005       | 20.34491933480445 |
	| 90006       | 21.56930375425860 |
	| ...         | ...               |
	+-------------+-------------------+
*/

Theory part: http://www.movable-type.co.uk/scripts/latlong.html
and the formula itself http://en.wikipedia.org/wiki/Haversine_formula

<?php
		$host_name = 'localhost';
		$database = 'db1';
		$user_name = 'root';
                $password = 'pswd';

                    $zipcode = $_POST['zipcode'];
                    $distance = $_POST['distance'];
                    
                    // Create connection
                    $conn = new mysqli($host_name, $user_name, $password, $database);
                    // Check connection
                    if ($conn->connect_error) {
                        die("Connection failed: " . $conn->connect_error);
                    } 

                    $sql = "SELECT * FROM zipcodeus WHERE zipcode = '$zipcode'";
                    $result = $conn->query($sql);

                    if ($result->num_rows > 0) {
                        // output data of each row
                       while($row = $result->fetch_assoc()) {
                            $lat1 = $row["latitude"];
                            $lon1 = $row["longitude"];
                           // echo 
                          //  "zipcode: " . $row["zipcode"]. 
                         //  "latitude: " . $row["latitude"]. 
                         //   "longitude: " . $row["longitude"]. 
                         //   " - city: " . $row["city"]. 
                          //  " - state: " . $row["name_state"]. "<br>";
                            }

                    } else {
                        echo "0 results";
                    }
                    $query = "SELECT *, ( 3959  * acos( cos( radians($lat1) ) 
                                                * cos( radians( latitude ) ) 
                                                * cos( radians( longitude ) 
                                                - radians($lon1) ) 
                                                + sin( radians($lat1) ) 
                                                * sin( radians( latitude ) ) ) ) 
                                                AS distance
                        FROM zipcodeus
                        HAVING distance < $distance;";

                        $print = $conn->query($query);

                        if ($print->num_rows > 0) {
                            // output data of each row
                            while($row = $print->fetch_assoc()) {
                                echo "zipcode: " 
                                . $row["zipcode"]. "latitude: " 
                                . $row["latitude"]. "longitude: " 
                                . $row["longitude"]. " - city: " 
                                . $row["city"]. " - state: " 
                                . $row["name_state"]. "<br>";
                            }
                        } else {
                            echo "0 results";
                        }
                        $conn->close();

                ?>

`
Live test
@vinaeoua

what is 3959

@sujit-thoughti very good question. 3959 is the radius of our planet (Earth) in miles according to IUGG standard. You can read more about it here: https://en.wikipedia.org/wiki/Earth_radius.

P.S. If you will even have to get list of zip codes within a specific distance on the Mars, you can replace 3959 with 2106.1

Hey, I tried this formula with ZipCode 39564:
@location_lat = 30.400640,
@location_lon = -88.758255

and it gives me this error:

It runs fine with the others that I've tested. Any idea why?
Thanks!

PS: I Rounded up to 5 decimal points in the formula and it worked, the precision decreased just a bit.

@stsibel SELECT zipcode, ( 3959 * acos( cos( radians(@location_lat) ) * cos( radians( latitude ) ) * cos( radians( longitude ) - radians(@location_lon) ) + sin( radians(@location_lat) ) * sin( radians( latitude ) ) ) ) AS distance FROM zipcodes HAVING distance < 25;

could you please tell me what value do i need to place in latitude? do we need to pass the same value which we are assigning in set operation.

thanks