[postgis-devel] Issue 139 in postgis: Default selectivity returned when geometry used for restricted join comes from another table, but accurate when from WKT

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Comment #1 on issue 139 by lr1234567: Default selectivity returned when  
geometry used for restricted join comes from another table, but accurate  
when from WKT
http://code.google.com/p/postgis/issues/detail?id=139

Just to add my 2 cents.

I tested the above on "POSTGIS="1.3.5" GEOS="3.0.3-CAPI-1.4.2" PROJ="Rel.  
4.6.1, 21
August 2008" USE_STATS", PostgreSQL 8.3.7

  The above two return in about the same speed (though plans are very  
different --
(the _ST_Contains goes into a nested loop for the non constant geometry )  
but the &&
is applied first non-nested and both timings are about the same on my box  
92 ms)

But this one even on my 8.3.7 performs really badly (5-6 times worse than  
the above
queries - 600 ms) which is closer to what Robert was trying to do) and  
bizarrely
doesn't even try to use an index.  So there seems to be a distinct  
disadvantage to
doing subselects like this.

SELECT
  count(*)
FROM
  points
  where ST_Contains((SELECT shape FROM shapes WHERE shape_id = 1), point);

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