PostgreSQL calculate distance between two points without using PostGIS

You can using, something like this:

select SQRT(POW(69.1 * (latitude::float -  p_lat::float), 2) +     POW(69.1 * (p_lon::float - longitude::float) * COS(latitude::float / 57.3), 2))

In this:

(latitude, Longitude) point 1.

(p_lat, p_lon) point 2

I found a function that could help you.

Font: geodatasource

Passed to function:
lat1, lon1 = Latitude and Longitude of point 1 (in decimal degrees)
lat2, lon2 = Latitude and Longitude of point 2 (in decimal degrees)
unit = the unit you desire for results
where: 'M' is statute miles (default)
'K' is kilometers
'N' is nautical miles

CREATE OR REPLACE FUNCTION calculate_distance(lat1 float, lon1 float, lat2 float, lon2 float, units varchar)RETURNS float AS $dist$    DECLARE        dist float = 0;        radlat1 float;        radlat2 float;        theta float;        radtheta float;    BEGIN        IF lat1 = lat2 OR lon1 = lon2            THEN RETURN dist;        ELSE            radlat1 = pi() * lat1 / 180;            radlat2 = pi() * lat2 / 180;            theta = lon1 - lon2;            radtheta = pi() * theta / 180;            dist = sin(radlat1) * sin(radlat2) + cos(radlat1) * cos(radlat2) * cos(radtheta);            IF dist > 1 THEN dist = 1; END IF;            dist = acos(dist);            dist = dist * 180 / pi();            dist = dist * 60 * 1.1515;            IF units = 'K' THEN dist = dist * 1.609344; END IF;            IF units = 'N' THEN dist = dist * 0.8684; END IF;            RETURN dist;        END IF;    END;$dist$ LANGUAGE plpgsql;

And you can use like below:

SELECT calculate_distance(32.9697, -96.80322, 29.46786, -98.53506, 'M');SELECT calculate_distance(32.9697, -96.80322, 29.46786, -98.53506, 'K');SELECT calculate_distance(32.9697, -96.80322, 29.46786, -98.53506, 'N');