point types in "DISTINCT" queries - Mailing list pgsql-general

From Jonathan S. Katz
Subject point types in "DISTINCT" queries
Date
Msg-id 9419BBB1-4858-4DC0-9FD8-733BAC99CF03@excoventures.com
Whole thread Raw
Responses Re: point types in "DISTINCT" queries
List pgsql-general
Hi,

I am running PostgreSQL 9.0.4 and I am getting an error with a SELECT DISTINCT query that contains a point type in the SELECT clause.  To be more specific, a query such as:

-- explicit declaration that it's a point type
SELECT DISTINCT a.geocode::point 
FROM a
WHERE a.region = 'x';

Will return the error:

ERROR: could not identify an equality operator for type point

I read the notes about how point types do not have "=" defined for them, but "~=" aka the "same as" operator (http://www.postgresql.org/docs/9.0/static/functions-geometry.html).  For points, I would treat ~= as equality.  I tried creating my own equality operator based on that:

CREATE OR REPLACE FUNCTION point_equality(point, point) RETURNS bool
   AS 'SELECT $1 ~= $2;'
   LANGUAGE SQL;

CREATE OPERATOR = (
   LEFTARG = point,
   RIGHTARG = point,
   PROCEDURE = point_equality,
   COMMUTATOR = =
);

And when I ran the query again:

ERROR: could not identify an equality operator for type point

I looked into the mailing list archives and found a potential answer on this thread: http://archives.postgresql.org/pgsql-general/2009-10/msg01122.php However I wanted to see if it was still necessary that I would need the complete btree operator class to run such a query.  Are there plans to have a defined "=" operator on the point type?  I can understand how the other geometric types, "=" would represent area, but AFAIK I think "=" could be safely applied on a point type (and i realize I could submit a patch for that :-) maybe depending on the resolution to this / refreshing my C...).

Is there possibly a relatively quick solution to this issue?

Thanks!

Jonathan

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