[postgis-tickets] [PostGIS] #3598: "&&" missing
PostGIS
trac at osgeo.org
Tue Jul 12 03:59:59 PDT 2016
#3598: "&&" missing
---------------------------+---------------------------
Reporter: jidanni | Owner: robe
Type: defect | Status: new
Priority: medium | Milestone: PostGIS 2.2.3
Component: documentation | Version: 2.2.x
Keywords: |
---------------------------+---------------------------
In file:///usr/share/doc/postgis-doc/postgis.html#idm2251
we see:
----
''We can avoid this by using the && operator to reduce the number of
distance calculations required:''
{{{
SELECT the_geom
FROM geom_table
WHERE ST_DWithin(the_geom, ST_MakeEnvelope(90900, 190900, 100100,
200100,312), 100)
}}}
''This query selects the same geometries, but it does it in a more
efficient way. Assuming there is a GiST index on the_geom, the query
planner will recognize that it can use the index to reduce the number of
rows before calculating the result of the ST_distance() function. Notice
that the ST_MakeEnvelope geometry which is used in the && operation is a
200 unit square box centered on the original point - this is our "query
box". The && operator uses the index to quickly reduce the result set
down to only those geometries which have bounding boxes that overlap the
"query box". Assuming that our query box is much smaller than the
extents of the entire geometry table, this will drastically reduce the
number of distance calculations that need to be done.''
------
But there is no "&&".
--
Ticket URL: <https://trac.osgeo.org/postgis/ticket/3598>
PostGIS <http://trac.osgeo.org/postgis/>
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