[postgis-users] whats the different between ST_Extent() and ST_Estimated_Extent()

[Mike Toews]

ST_Estimated_Extent for large tables can be faster, since it uses
cached statistics from the last VACUUM ANALYZE. The time difference is
not evident with only a few rows of data.

Also, ST_Estimated_Extent only works on tables, and not VIEWs (an
error is returned). I had to overwrite the ST_Estimated_Extent
function to use ST_Extent on one server that uses the AutoCAD Map 3D
FDO PostGIS Provider, since it had the ST_Estimated_Extent command
hard-wired in the layer-load for both views and tables (resulting in
instability AutoCAD).

-Mike

On 27 June 2010 23:32, nguyen liem <liemnguyendl at gmail.com> wrote:
> Hi All,
>
> I have 2 queries:
> SELECT ST_Extent(point) FROM schema.mytable;
> SELECT ST_Estimated_Extent('schema', 'mytable', 'point');
>
> 2 queries above were returned for me same result (BOX2D):
> "BOX(11.1806726455688 55.3748893737793,24.1317653656006 67.8551025390625)"
> I don't know what is the different between 2 functions, should I use
> ST_Extent or ST_Estimated_Extent in this case.
> And ... Will be better, if you explain me when we need to use ST_Extent and
> when we need to use ST_Estimated_Extent  ;)
>
> Cheers.
>
> --
> Liem Nguyen
> Developer
> Axon Active Corp.
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