[postgis-tickets] [PostGIS] #3344: Unnecessary use of table/possible speed improvement

[PostGIS]

#3344: Unnecessary use of table/possible speed improvement
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 Reporter:  postgispaul  |      Owner:  pramsey
     Type:  enhancement  |     Status:  new
 Priority:  medium       |  Milestone:
Component:  postgis      |    Version:  2.1.x
 Keywords:               |
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 Situation:
 - table polygons with geomety and a nameid
 - table names with id and name

 query-plan for
 SELECT st_extent(geometry) FROM polygons
 gives me a sequential scan over the polygons table

 but the query-plan for

 SELECT st_extent(geometry)
 FROM polygons
 LEFT JOIN names ON names.id=polygons.nameid

 gives me a sequential scan over polygons and after that a nested loop
 fetching the name from the names table.

 This last step seems really superfluous as the extent doesn't change if a
 left join is involved or not.

 This is particularly annoying when using postgresql/postgis with qgis if
 the left join is against a slow source, because qgis often does a SELECT
 st_extent

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3344>
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