find the nearest location by latitude and longitude in postgresql - sql

Question

Hi i'm trying find the nearest location by latitude and longitude in postgresql database.But when i run the below query it showing column distance does not exists.
ERROR: column "distance" does not exist
LINE 1: ... ) ) ) AS distance FROM station_location HAVING distance <...
^
********** Error **********
ERROR: column "distance" does not exist
SQL state: 42703
Character: 218
CREATE TABLE station_location
(
id bigint NOT NULL DEFAULT nextval('location_id_seq'::regclass),
state_name character varying NOT NULL,
country_name character varying NOT NULL,
locality character varying NOT NULL,
created_date timestamp without time zone NOT NULL,
is_delete boolean NOT NULL DEFAULT false,
lat double precision,
lng double precision,
CONSTRAINT location_pkey PRIMARY KEY (id)
)
SELECT *,( 3959 * acos( cos( radians(6.414478) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians(12.466646) ) + sin( radians(6.414478) ) * sin( radians( lat ) ) ) ) AS distance
FROM station_location
HAVING distance < 5
ORDER BY distance
LIMIT 20;

Answer 1

PostGIS
Don't store lat and long on a table like that. Instead use an PostGIS geometry or geography type.
CREATE EXTENSION postgis;
CREATE TABLE foo (
geog geography;
);
CREATE INDEX ON foo USING gist(geog);
INSERT INTO foo (geog)
VALUES (ST_MakePoint(x,y));
Now when you need to query it, you can use KNN (<->) which will actually do this on an index.
SELECT *
FROM foo
ORDER BY foo.geog <-> ST_MakePoint(x,y)::geography;
In your query, you explicitly have HAVING distance < 5. You can do that on the index too.
SELECT *
FROM foo
WHERE ST_DWithin(foo.geog, ST_MakePoint(x,y)::geography, distance_in_meters)
ORDER BY foo.geog <-> ST_MakePoint(x,y)::geography;
This ensure that nothing is returned if all points lie outside of distance_in_meters.
Furthermore x and y are decimal numbers ST_MakePoint(46.06, 14.505)

Answer 2

select * from (
SELECT *,( 3959 * acos( cos( radians(6.414478) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians(12.466646) ) + sin( radians(6.414478) ) * sin( radians( lat ) ) ) ) AS distance
FROM station_location
) al
where distance < 5
ORDER BY distance
LIMIT 20;

Answer 3

You can use PostgreSQL's cube and earthdistance extensions.
Enable them like this:
CREATE EXTENSION cube;
CREATE EXTENSION earthdistance;
Let's say your current location is 35.697933, 139.707318. Then your query will be something like this:
SELECT *, point(35.697933, 139.707318) <#> (point(longitude, latitude)::point) as distance
FROM station_location
-- WHERE (point(35.697933, 139.707318) <#> point(longitude, latitude)) < 3
ORDER BY distance;
Please note that the distance is in miles (by default).

Answer 4

See this gist, you will find how to declare a DOMAIN on the point type and how to override the distance operator to return the orthodromic distance.
Declare a latlong type inherited from point:
CREATE DOMAIN latlong AS point CHECK (VALUE[0] BETWEEN -90.0 AND 90.0 AND VALUE[1] BETWEEN -180 AND 180);
The orthodromic distance in kilometers (distance on a sphere with the earth radius):
CREATE OR REPLACE FUNCTION orthodromic_distance(latlong, latlong) RETURNS float AS $_$
SELECT acos(
sin(radians($1[0]))
*
sin(radians($2[0]))
+
cos(radians($1[0]))
*
cos(radians($2[0]))
*
cos(radians($2[1])
-
radians($1[1]))
) * 6370.0;
$_$ LANGUAGE sql IMMUTABLE;
Override the distance operator <-> using this function when used with latlongs:
CREATE OPERATOR <-> ( PROCEDURE = orthodromic_distance
, LEFTARG = latlong, RIGHTARG = latlong
);
Now in your SQL queries, to find the nearest entities:
WITH
station_distance AS (
SELECT
id AS station_id,
point(lat, long)::latlong <-> point(6.414478, 12.466646)::latlong AS distance
FROM station_location
WHERE NOT is_deleted
)
SELECT
sl.state_name,
sl.country_name,
sl.locality,
point(sl.lat, sl.long)::latlong AS coordinates,
sd.distance
FROM
station_location sl
JOIN station_distance sd
ON sd.station_id = sl.id
ORDER BY
distance ASC
LIMIT 10
You probably want to store the position lat and long in the same field using the latlong type.

Answer 5

The manual clarifies :
An output column's name can be used to refer to the column's value in
ORDER BY and GROUP BY clauses, but not in the WHERE or HAVING clauses;
there you must write out the expression instead.