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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">I just noticed something interesting, perhaps its trivial and well understood, but this is the first time I figured it out (older postgis and postgresql to boot). I am doing a
spatial containment query on two tables, table "a" being a point table in SRID 4326, with GIST index, and table "b" being a polygon with GIST index in SRID 26918, using the "transform" function to bring them into a common projection. If I apply the transform
to the polygon layer, the query planner (and indeed the query) is verrrry slow, whereas, if I apply the transform to the point layer, things go along much more swiftly. Now I know, so I just thought I'd share, if anyone has any suggestions of course, I would
be delighted to hear them.<br>
<br>
/r/b<br>
<br>
For example:<br>
postgis_version<br>
---------------------------------------<br>
1.5 USE_GEOS=1 USE_PROJ=1 USE_STATS=1 / PostgreSQL 8.3<br>
<br>
<br>
QUERY PLAN<br>
-----------------------------------------------------------------------------------------------<br>
Nested Loop (cost=0.00..16874.46 rows=75352 width=82234)<br>
Join Filter: contains(b.the_geom, transform(a.the_geom, 26918))<br>
-> Seq Scan on sc_cbp53 b (cost=0.00..65.09 rows=1 width=81986)<br>
Filter: ((riverseg)::text = 'PS3_5100_5080'::text)<br>
-> Seq Scan on vpdes_discharge_no_ms4_cache a (cost=0.00..13418.55 rows=226055 width=248)<br>
(5 rows)<br>
<br>
vpdes=# explain select * from vpdes_discharge_no_ms4_cache as a, sc_cbp53 as b where contains(transform(b.the_geom,4326),a.the_geom); QUERY PLAN<br>
-----------------------------------------------------------------------------------------------<br>
Nested Loop (cost=0.00..18815543.18 rows=109033851 width=82234)<br>
Join Filter: contains(transform(b.the_geom, 4326), a.the_geom)<br>
-> Seq Scan on vpdes_discharge_no_ms4_cache a (cost=0.00..13418.55 rows=226055 width=248)<br>
-> Seq Scan on sc_cbp53 b (cost=0.00..61.47 rows=1447 width=81986)<br>
(4 rows)<br>
<br>
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