“Calculating distance using MySQL” is a very useful blog post for everyone who works with geographical location data and MySQL. It shows a simple example of how to calculate the distance between two coordinates on a sphere (Earth in particular) within the MySQL itself.
SELECT ST_Distance_Sphere( point(-87.6770458, 41.9631174), point(-73.9898293, 40.7628267) );
The above will return 1148978.6738241839, which is the distance between the two points in meters.
This functionality is available since MySQL 5.7. Have a look at the documentation of the spacial convenience functions.
MariaDB has similar functionality, but with a slightly different function names. Use ST_DISTANCE() instead of ST_Distance_Sphere(). Have a look at this blog post for more details.