[postgis-users] Slow spatial join with subquery and UNION

[Håvard Wahl Kongsgård]

SELECT COUNT(DISTINCT SPATIAL_POINTS_1.id) from SPATIAL_POINTS_1 as
SPATIAL_POINTS_1 Inner join (Select geom from SPATIAL_POINTS_2 UNION SELECT
geom from SPATIAL_POINTS_3) as SPATIAL_POINTS_X on
ST_DWithin(SPATIAL_POINTS_1.the_geom, SPATIAL_POINTS_X.geom, 500)

This UNION subquery is very slow, there are indexes for each geom. If I
skip the UNION it's much faster.

Is there an alternative way to do this?
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