mySQL longitude and latitude query for other rows within x mile radius

Question

I have a database populated with roughly 10k rows currently. All of them have a longitude/latitude based on the center of a zipcode. I found a query that I am now attempting to expand on, but all in all it works well to a point. However, in my example below I am trying to find things within a 25 mile radius, which in all seems to work for the most part. Most of my results do yield within the 25 mile criteria, however I am getting a handful that are way off anything from 86 miles to 800 miles off the mark.

Example: This is my center lat/lon: 37.2790669,-121.874722 = San Jose, CA Im getting results like: 33.016928,-116.846046 = San Diego, CA which is about 355 miles from San Jose.

my current query looks like:

SELECT *,(((acos(sin(($lat*pi()/180)) * sin((`latitude`*pi()/180))+cos(($lat*pi()/180))
* cos((`latitude`*pi()/180)) * cos((($lon - `longitude`)*pi()/180))))*180/pi())*60*1.1515)
AS `distance` FROM `geo_locations` HAVING `distance` <= 25 ORDER BY `distance` ASC"

Answer 1

Here is the query I use on the store locator I work with:

SELECT
    `id`,
    (
        6371 *
        acos(
            cos( radians( :lat ) ) *
            cos( radians( `lat` ) ) *
            cos(
                radians( `long` ) - radians( :long )
            ) +
            sin(radians(:lat)) *
            sin(radians(`lat`))
        )
    ) `distance`
FROM
    `location`
HAVING
    `distance` < :distance
ORDER BY
    `distance`
LIMIT
    25

:lat and :long are the points the passed by the user where lat and long are the points stored in the database.

The :distance is measured in miles, in the working version of the code the :distance is actually pulled from a drop down ranging from 10-50 miles

Changing the code to work with kilometers can be accomplished by changing 3959 (the distance from the center of the earth to its surface in miles) to 6371 (3959 miles converted to kilometers) thanks to joshhendo for that solution.