From 8ec230fb6bfe84efd214651975b5c53bbfd67d3b Mon Sep 17 00:00:00 2001 From: Regina Obe Date: Wed, 8 May 2013 05:18:31 +0000 Subject: [PATCH] #2242: Clarify behavior of ST_Union with NULLS git-svn-id: http://svn.osgeo.org/postgis/trunk@11383 b70326c6-7e19-0410-871a-916f4a2858ee --- doc/reference_processing.xml | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/doc/reference_processing.xml b/doc/reference_processing.xml index af17d0db4..bd50c4509 100644 --- a/doc/reference_processing.xml +++ b/doc/reference_processing.xml @@ -2875,11 +2875,11 @@ MULTILINESTRING((1 3 2.75,1 4 2),(1 1 3,1 2 2.25)) from a set of geometries. The ST_Union() function is an "aggregate" function in the terminology of PostgreSQL. That means that it operates on rows of data, in the same way the SUM() and AVG() - functions do. + functions do and like most aggregates, it also ignores NULL geometries. Non-Aggregate version: This function returns a geometry being a union of two input geometries. Output type can be a MULTI*, NON-MULTI or - GEOMETRYCOLLECTION. + GEOMETRYCOLLECTION. If any are NULL, then NULL is returned. ST_Collect and ST_Union are often interchangeable. ST_Union is in general orders of magnitude slower than ST_Collect -- 2.40.0