[postgis-users] how to define an alias for && operator?

[Jean-Pierre Quirion]

--- Mark Cave-Ayland <m.cave-ayland at webbased.co.uk> a écrit :

> 
> > -----Original Message-----
> > From: postgis-users-bounces at postgis.refractions.net 
> > [mailto:postgis-users-bounces at postgis.refractions.net] On 
> > Behalf Of Jean-Pierre Quirion
> > Sent: 04 November 2005 15:14
> > To: PostGIS Users Discussion
> > Subject: RE: [postgis-users] how to define an alias for && operator?
> 
> (cut)
> 
> > The "OPERATOR 3  <<< RECHECK," line has been added. And this 
> > does not work. Apparently you can not reuse a 
> > strategy_number, is this right (3 in this case). [My 
> > assumptions are based on 
> > http://www.postgresql.org/docs/8.0/interactive/sql-createopclass.html]
> > Our problem is not the operator (it works), but the 
> > association with an index aka operator class. If we used a 
> > new strategy number like 13, we would have to define a new 
> > strategy in "lwgeom_gist.c" . I am looking for an easier solution.
> > 
> > Jean-Pierre
> 
> 
> Hi Jean-Pierre,
> 
> The operator classes are defined in terms of strategy number so you will be
> unable to do this. The actual modifications in lwgeom_gist.c shouldn't be
> that bad though - you could probably get away with just defining a new
> strategy around line 78, e.g.
> 
> #define RTNewOverlapStrategyNumber		13
> 
> And then simply replace the two occurences of "case
> RTOverlapStrategyNumber:" with
> 
> case RTOverlapStrategyNumber:
> case RTNewOverlapStrategyNumber:
> 
> You should then be able to add your operator by including the following line
> in your operator class:
> 
> "OPERATOR 13  <<< RECHECK"
> 
> Kind regards,
> 
> Mark.

Mark,
Thanks for the hint. If we modified lwgeom_gist.c or any other file, updates of PostGis would be
less straight forward.

We found - some minutes ago- the following solution for our original problem (avoiding && in a
query).
You probably know that geometry_overlap() does not use the indexes but "&&" does. So we just
define a new function called "ampamp":

CREATE function ampamp(geometry,geometry) returns boolean as 'select $1 && $2' language sql;

The function ampamp() is as serviceable as geometry_overlap() but uses the same indexes as "&&"
does. 

Do you see any inconveniences? What is the reason that postgis does not include indexed versions
of the functions? Maybe nobodies uses the function instead of the operators.

Kind Regards
Jean-Pierre






	

	
		
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