Re: Pulling additional columns with aggregate

From: sub3 <steve@subwest.com>
Subject: [SQL] Pulling additional columns with aggregate
To: pgsql-sql@postgresql.org
Date: Thursday, October 8, 2009, 1:14 PM

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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