Optimize SQL query with 3 FOR loops - sql

Question

I have a fully working SQL query. However, it is very very slow. I am looking for a way to optimize it.
CREATE TABLE trajectory_geom (
id SERIAL PRIMARY KEY,
trajectory_id BIGINT,
user_id BIGINT,
geom GEOMETRY(Linestring, 4326)
);
INSERT INTO trajectory_geom (trajectory_id, user_id, geom)
SELECT
p.trajectory_id,
p.user_id,
ST_Transform(ST_MakeLine(p.geom), 4326)
FROM point p
GROUP BY p.trajectory_id
;
DO $$
DECLARE
urow record;
vrow record;
wrow record;
BEGIN
FOR wrow IN
SELECT DISTINCT(p.user_id) FROM point p
LOOP
raise notice 'User id: %', wrow.user_id;
FOR vrow IN
SELECT DISTINCT(p.trajectory_id) FROM point p WHERE p.user_id = wrow.user_id
LOOP
FOR urow IN
SELECT
analyzed_tr.*
FROM trajectory_start_end_geom analyzed_tr
WHERE
analyzed_tr.user_id = wrow.user_id
AND
ST_Intersects (
(
analyzed_tr.start_geom
)
,
(
SELECT g.geom
FROM trajectory_geom g
WHERE g.trajectory_id = vrow.trajectory_id
)
) = TRUE
LOOP
INSERT INTO trajectories_intercepting_with_starting_point (initial_trajectory_id, mathced_trajectory_id, user_id)
SELECT
vrow.trajectory_id,
urow.trajectory_id,
wrow.user_id
WHERE urow.trajectory_id <> vrow.trajectory_id
;
END LOOP;
END LOOP;
END LOOP;
END;
$$;
It has 3 loops...how can I avoid them?
Basically, I am looping all user IDs, for each user looping all trajectories and checking is trajectory interact with any other trajectory of this user.
Schema:
CREATE TABLE public.trajectory_start_end_geom
(
id integer NOT NULL DEFAULT nextval('trajectory_start_end_geom_id_seq'::regclass),
trajectory_id bigint,
user_id bigint,
start_geom geometry(Polygon,4326),
end_geom geometry(Polygon,4326),
CONSTRAINT trajectory_start_end_geom_pkey PRIMARY KEY (id)
)
WITH (
OIDS=FALSE
);
CREATE TABLE public.trajectory_geom
(
id integer NOT NULL DEFAULT nextval('trajectory_geom_id_seq'::regclass),
trajectory_id bigint,
user_id bigint,
geom geometry(LineString,4326),
CONSTRAINT trajectory_geom_pkey PRIMARY KEY (id)
)
WITH (
OIDS=FALSE
);
CREATE TABLE public.point
(
id integer NOT NULL DEFAULT nextval('point_id_seq'::regclass),
user_id bigint,
date date,
"time" time without time zone,
lat double precision,
lon double precision,
trajectory_id integer,
geom geometry(Geometry,4326),
CONSTRAINT point_pkey PRIMARY KEY (id)
)
WITH (
OIDS=FALSE
);

Answer 1

Try this SQL query. Hope this helps.
INSERT INTO trajectories_intercepting_with_starting_point
(initial_trajectory_id, mathced_trajectory_id, user_id)
SELECT
TG.trajectory_id AS first_trajectory_id,
TG2.trajectory_id AS last_trajectory_id,
TG.user_id
FROM Trajectory_geom AS TG
JOIN Trajectory_geom AS TG2 ON TG.user_id = TG2.user_id
AND TG.trajectory_id < TG2.trajectory_id
JOIN Trajectory_start_end_geom AS TSE ON TSE.trajectory_id = TG.trajectory_id
WHERE ST_Intersects(TSE.start_geom, TG2.geom) = TRUE

Answer 2

This should do the trick:
WITH vrow AS(
INSERT INTO trajectory_geom (trajectory_id, user_id, geom)
SELECT
p.trajectory_id,
p.user_id,
ST_Transform(ST_MakeLine(p.geom), 4326) AS geom
FROM point p
GROUP BY p.trajectory_id
RETURNING trajectory_id, user_id, geom
)
INSERT INTO trajectories_intercepting_with_starting_point (initial_trajectory_id, mathced_trajectory_id, user_id)
SELECT
vrow.trajectory_id,
urow.trajectory_id,
vrow.user_id
FROM trajectory_start_end_geom AS urow
JOIN vrow
ON urow.user_id = vrow.user_id
AND urow.trajectory_id <> vrow.trajectory_id
AND ST_Intersects(urow.start_geom, vrow.geom)
If you don't need insert into trajectory_geom eliminating it (and the CTE) will speed it up