On Wed, Jun 2, 2010 at 7:23 AM, Michael Diener <m.diener@gomogi.com> wrote:
> select sum(flaeche)/10000 as "greens HA" from green;
> result:
> Wrong Answer with this query
>
> select
> sum(green.flaeche)/10000 as "greens HA",
> sum (fairway.flaeche)/10000 as "fairway HA"
> from green, fairway;
It isn't easy to see but you are effectively joining green to fairway
using a cross project which product a Cartesian product.
you probably wanted this query:
SELECT (select sum(flaeche)/10000 from green) AS "greens HA",
(select sum(flaeche)/10000 from fairway) AS "fairway HA";
However, from what you've shown. I would wager that your database is
in need of some normalization. For example you could put both greens
and fair way into a single table like:
CREATE TABLE Lawns AS
SELECT flaech, "green"::VARCHAR AS lawntype
FROM green
UNION ALL
SELECT flaech, "fairway"::VARCHAR AS lawntype
FROM fairway;
Then you'd execute the following query:
SELECT lawntype, sum(flaech)/10000 AS "HA"
FROM Lawns
GROUP BY lawntype;
--
Regards,
Richard Broersma Jr.
Visit the Los Angeles PostgreSQL Users Group (LAPUG)
http://pugs.postgresql.org/lapug
