The <<->> operator returns the n-D (euclidean) distance between the
centroids of the bounding boxes of two geometries. Useful for doing
nearest neighbor approximate distance ordering.
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This operand will make use of n-D GiST indexes that may be available
on the geometries. It is different from other operators that use spatial
indexes in that the spatial index is only used when the operator is in
the ORDER BY clause. |
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Index only kicks in if one of the geometries is a constant (not in a
subquery/cte). e.g. 'SRID=3005;POINT(1011102 450541)'::geometry instead
of a.geom |
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Availability: 2.2.0 — KNN only available for PostgreSQL 9.1+