Find points within a distance using MySQL
Using GIS

Assuming MySQL 8+

SELECT u.*,
  ST_Distance(
    ST_SRID(Point(65.3234, 78.3232),4326), 
    ST_SRID(Point(u.lon,u.lat),4326)
  )
FROM Users AS u
WHERE ST_Intersects(
  ST_Buffer(ST_SRID(Point(65.3234, 78.3232),4326), 5000), 
  ST_SRID(Point(u.lon,u.lat),4326)
);


If you're not using MySQL 8+ you can't use ST_SRID(geom,SRID). Also, if you store GEOMETERY types on the table, rather than silly lat and long columns, this looks a lot cleaner.

SELECT u.*,
  ST_Distance(
    ST_SRID(Point(65.3234, 78.3232),4326), 
    u.geom
  )
FROM Users AS u
WHERE ST_Intersects(
  ST_Buffer(ST_SRID(Point(65.3234, 78.3232),4326), 5000), 
  u.geom
);