Hi,
I have 2 tables. I want to be able to calculate the closest value in one
(tempvalues), to the closest value in the other (points). This closest
point, I want to save into the table with its difference.
So if I have:
create table points (
id integer,
center double precision
);
insert into points values (1, 1),(2,4),(3,7),(4,12);
CREATE TABLE tempvalues (
id serial NOT NULL,
"value" double precision,
closest_point_id integer,
distance_to_point double precision,
CONSTRAINT tempvalues_pkey PRIMARY KEY (id),
CONSTRAINT tempvalues_closest_point_id_fkey FOREIGN KEY (closest_point_id)
REFERENCES points (id) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION
);
insert into tempvalues (value) values
(1.1),(2.2),(3.3),(4.4),(5.5),(6.6),(7.7),(8.8),(9.9),
(10.1),(11.1),(12.2),(13.3),(14.4),(15.5),(16.6),(17.7),(18.8),(19.9),(20.0);
I would like to see each row in tempvalues populated with the closest point
from points and its difference.
I know I can find the cartesian product of the 2 tables, and get the
distance between all values.
select tempvalues.id as tid, points.id as pid,
min(abs(points.center-tempvalues.value))
from points, tempvalues group by tempvalues.id,points.id order by tid,pid
But I can't figure out how to return the result w/only 1 row per
tempvalue.id (the minimum) and still get the id column from each table. Any
aggregate with force those columns out.
I would love to do something like:
update tempvalues set closest_point_id,distance_to_point from (above
query)
but haven't been able to figure this out. Any suggestions?
Thanks.
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