[HACKERS] How to deal with order by, group by, distinct for user-defined types

[Ruey-Lung Hsiao]

Hi,
  I implemented a user-defined type, say X, and when I want to do the 
following queries, Postgresql will complain

CREATE TABLE Table1 ( id integer, object X );
SELECT X, count(*) from Table1
GROUP BY X;
ERROR:  could not identify an ordering operator for type X
HINT:  Use an explicit ordering operator or modify the query.
  My question is: how do I find or define ordering operators for my 
user-defined type?

Thanks.
Ruey-Lung Hsiao
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