Some notes on PostGis

gis.sql

-- Creates the table
CREATE TABLE geom_points ( 
  id_pk INTEGER PRIMARY KEY
);

-- Adds the columns
SELECT AddGeometryColumn('geom_points','coordinates','4326','POINT',2); -- (long, lat)

-- Inserts the Latitude and Longitude from Geography to Geometry. (long, lat)
INSERT INTO geom_points(id_pk, coordinates)
VALUES(2, ST_SetSRID(ST_MakePoint(121.052030, 14.575008), 4326), 4326));

-- Snippet to convert from geography to geometry. (long, lat)
ST_SetSRID(ST_MakePoint(121.052030, 14.575008), 4326);

-- Simple search by radius (long, lat)
select * from geom_points 
where ST_DWithin(
  coordinates::geography,                                                  -- the column to search 
  ST_SetSRID(ST_MakePoint(121.052031, 14.575008), 4326)::geography,        -- the center
  0.19                                                                     -- radius
)

-- Get result as lat long (http://gis.stackexchange.com/a/91321)
select 
ST_X(ST_Transform(coordinates, 4326)) AS Longitude,
ST_Y(ST_Transform(coordinates, 4326)) AS Latitude
from geom_points 
where ST_DWithin(
  coordinates::geography, 
  ST_SetSRID(ST_MakePoint(14.575008, 121.052031), 4326)::geography, 
  0.19
)