From: Regina Obe <lr@pcorp.us>
Date: Wed, 8 May 2013 05:18:31 +0000 (+0000)
Subject: #2242: Clarify behavior of ST_Union with NULLS
X-Git-Tag: 2.1.0beta2~44
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=8ec230fb6bfe84efd214651975b5c53bbfd67d3b;p=postgis

#2242: Clarify behavior of ST_Union with NULLS

git-svn-id: http://svn.osgeo.org/postgis/trunk@11383 b70326c6-7e19-0410-871a-916f4a2858ee
---

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.</para>
+		functions do and like most aggregates, it also ignores NULL geometries.</para>
 
 	<para>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.</para>
+		GEOMETRYCOLLECTION. If any are NULL, then NULL is returned.</para>
 
 	<note><para>ST_Collect and ST_Union are often interchangeable.
 		ST_Union is in general orders of magnitude slower than ST_Collect