mySQL- show nearest stores with no range or limit

Question

I have got a very basic store locator script. which the user enters postcode/zip-code that is converted to lat and long and then searched in the database to find the nearest stores.

my current SQL:

SELECT id, ( 3959 * acos( cos( radians(37) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians(-122) ) + sin( radians(37) ) * sin( radians( lat ) ) ) ) AS distance
FROM markers
HAVING distance < 500
ORDER BY distance
LIMIT 0 , 100;

As you can see this does work, but its limited to a range of 500 miles, i want to remove the limit. if i try remove HAVING distance < 500 , the distance is returned as NULL.

I need the results to says Store name XX miles away.

Another question, can this query be optimized? i have lat and long cols in the database as index.

Answer 1

The distance is NULL because some of your records have NULL values for lat and/or lng. You can add:

HAVING distance is not null

until you fix the problem.

If you want to optimize the query, then think about using the geospatial extensions (the documentation is here).

Answer 2

You can Query :

// Search the rows in the markers table
$query = sprintf("SELECT address, name, lat, lng, ( 3959 * acos( cos( radians('%s') ) * cos( radians( lat ) ) * cos( radians( lng ) - radians('%s') ) + sin( radians('%s') ) * sin( radians( lat ) ) ) ) AS distance FROM markers HAVING distance < '%s' ORDER BY distance LIMIT 0 , 20",
  mysql_real_escape_string($center_lat),
  mysql_real_escape_string($center_lng),
  mysql_real_escape_string($center_lat),
  mysql_real_escape_string($radius));
$result = mysql_query($query);