Hi all,
I have come across a unexpected behavior.
You can see full detail on an issue on the QGEP project in Github :
Basically, we have this view with some LEFT JOIN :
http://paste.debian.net/982003/We have indexes on some fields ( foreign keys, and a GIST index for the PostGIS geometry field)
If I use the raw SQL defining the view, and add a WHERE clause like:
WHERE "progression_geometry" && st_makeenvelope(1728327.03249295568093657,8240789.26074041239917278,1728608.10987572139129043,8240958.16933418624103069,3949)
the query plan is "as expected", as it is using the spatial index (and others too). This query gets 100 lines from a "main" table containing 20000 lines (and child tables having more). It is pretty fast and "low cost"
See the query plan:
When we call the WHERE on the view:
EXPLAIN (ANALYZE, COSTS, VERBOSE, BUFFERS)
SELECT *
FROM "qgep"."vw_qgep_reach"
WHERE "progression_geometry" && st_makeenvelope(1728327.03249295568093657,8240789.26074041239917278,1728608.10987572139129043,8240958.16933418624103069,3949)
The query plan is "wrong", as PostgreSQL seems to consider it should do a seq scan on the tables, and only afterwards filter with the WHERE:
The query takes about 1 second instead of less than 100ms.
Do you have any hint on this kind of issue ?
Thanks in advance
Regards,
Michaël