[postgis-devel] PG7.4 ordering operator

[strk]

Ops.. I forgot to tell the info source:
http://www.postgresql.org/docs/7.4/interactive/xindex.html

Another thing: in order to make a default btree operator class
a geometry_compare function will be also needed. 

--strk;

strk wrote:
> 
> Found the problem:
> > When there is no default [B-tree] operator class for a data type,
> > you will get errors like "could not identify an ordering operator"
> > if you try to use these SQL features [DISTINCT, GROUP BY, ORDER BY]
> > with the data type. 
> > [...]
> > Note:  In PostgreSQL versions before 7.4, sorting and grouping operations
> > would implicitly use operators named =, <, and >. The new behavior of
> > relying on default operator classes avoids having to make any assumption
> > about the behavior of operators with particular names. 
> 
> So we need to define a default b-tree operatoc class in
> postgis_sql_74_end.sql.in
> 
> --strk;
> 
> strk wrote:
> > Testing postgis support in PG7.4 (2003-11-11)
> > I've encountered to this problem:
> > 
> >         ERROR:  could not identify an ordering operator for type geometry
> >         HINT:  Use an explicit ordering operator or modify the query.
> > 
> > Whenever I issue one of these commands:
> > 
> > 	gis=# select the_geom from table1 UNION select the_geom from table2;
> > 	gis=# select DISTINCT the_geom from table1;
> > 	gis=# select the_geom from table1 ORDER BY the_geom;
> > 
> > Operators '<', '>', '=' are available:
> > 
> > 	 oprname | leftoperand | rightoperand
> > 	---------+-------------+--------------
> > 	 <<      | geometry    | geometry
> > 	 &<      | geometry    | geometry
> > 	 &&      | geometry    | geometry
> > 	 &>      | geometry    | geometry
> > 	 >>      | geometry    | geometry
> > 	 ~=      | geometry    | geometry
> > 	 @       | geometry    | geometry
> > 	 ~       | geometry    | geometry
> > 	 =       | geometry    | geometry
> > 	 <       | geometry    | geometry
> > 	 >       | geometry    | geometry
> > 	(11 rows)
> > 
> > Previous PG versions does not show this problem.
> > Any hint on what might be missing ?
> > 
> > --strk;
> > 
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