[postgis-users] Extent on multiple tables

[Mark Cave-Ayland]

Hi Lars/strk,

> -----Original Message-----
> From: postgis-users-bounces at postgis.refractions.net 
> [mailto:postgis-users-bounces at postgis.refractions.net] On 
> Behalf Of strk at refractions.net
> Sent: 21 October 2005 11:22
> To: postgis-users at postgis.refractions.net
> Subject: Re: [postgis-users] Extent on multiple tables
> 
> 
> You might try:
> 
> 	select extent(g) from (
> 		select the_geom from table1
> 		union all
> 		select the_geom from table2
> 	) as foo;

Isn't there an extent() missing from each of the individual tables?
Otherwise you have to load all the geometries from all the tables into
memory before you calculate the overall extent, rather than working on a per
table basis. I would suggest something like:

select extent(g) from (
	select extent(the_geom) AS g FROM table1
	union all
	select extent(the_geom) AS g FROM table2
) as foo;

Or if you can live with slightly inaccurate extents then the super-fast
estimated_extent() version would look like:

select extent(g) from (
	select estimated_extent(the_geom) AS g FROM table1
	union all
	select estimated_extent(the_geom) AS g FROM table2
) as foo;


Kind regards,

Mark.

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