SELECT DISTANCE

gistfile1.sql

SELECT *
FROM (SELECT *,
((2 * 3960 * 
		ATAN2(
			SQRT(
				POWER(SIN((RADIANS(47.470779 - latitude))/2), 2) +
				COS(RADIANS(latitude)) *
				COS(RADIANS(47.470779 )) *
				POWER(SIN((RADIANS(-87.890699 - longitude))/2), 2)
			),
			SQRT(1-(
				POWER(SIN((RADIANS(47.470779 - latitude))/2), 2) +
				COS(RADIANS(latitude)) *
				COS(RADIANS(47.470779 )) *
				POWER(SIN((RADIANS(-87.890699 - longitude))/2), 2)
			))
		)
	) * 1.609344) AS distance
FROM zip_codes) as tmp_table
WHERE distance < 50