How to find all street intersections in my city using Postgis

Question

Hi, I have to find all street intersections, I wrote below code but it returns duplicate rows. Does anyone have an idea why or khnows how to correct it!! Thank you for your help.

DROP TABLE IF EXISTS toto;

CREATE TABLE toto(
gid serial primary key,
nom_voie1 varchar(50),
nom_voie2 varchar(50),
geom_inter geometry(Geometry,4326)
);

CREATE INDEX ON toto using gist (geom_inter);

INSERT INTO toto(nom_voie1, nom_voie2, geom_inter)
SELECT a.nom_voie, b.nom_voie, ST_Intersection(a.geom, b.geom)
FROM reseau_routier AS a , reseau_routier AS b 
WHERE ST_Intersects(a.geom,b.geom) 
  AND ST_Touches(a.geom, b.geom) 
  AND a.gid < b.gid 
  AND a.nom_voie <> b.nom_voie; 

Answer 1

You are getting duplicated because of the JOIN on reseau_routier.

You can remove duplicated with:

INSERT INTO toto(nom_voie1, nom_voie2, geom_inter)
SELECT a.nom_voie, b.nom_voie, ST_Intersection(a.geom, b.geom)
FROM reseau_routier AS a , reseau_routier AS b 
WHERE ST_Intersects(a.geom,b.geom) 
  AND ST_Touches(a.geom, b.geom) 
  AND a.gid < b.gid 
  AND a.nom_voie <> b.nom_voie
GROUP BY  a.nom_voie, b.nom_voie, ST_Intersection(a.geom, b.geom);

But these duplicated are the sign of a malformed query. With a full data sample it would be easier to give you the perfect query.