[postgis-tickets] [PostGIS] #4991: st_union of single row should keep the row intact

[PostGIS]

#4991: st_union of single row should keep the row intact
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  Reporter:  michal   |      Owner:  pramsey
      Type:  defect   |     Status:  closed
  Priority:  medium   |  Milestone:  PostGIS 3.1.5
 Component:  postgis  |    Version:  3.1.x
Resolution:  invalid  |   Keywords:
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Comment (by robe):

 ST_MemUnion hasn't been touched in eons and does a state
 ST_Union(geom1,geom2).  At a glance ST_Union(geom1,geom2) returns the non-
 null geometry if one of the geometries is null (as would be the case with
 an ST_MemUnion with only one geometry).  I'm surprised this doesn't use
 ST_UnaryUnion :) so there is another function we need to clarify the
 behavior.

 At anyrate ST_Union agg is generally much more efficient than ST_MemUnion
 if you have many geometries.  That said I'd go with
 ST_LineMerge(ST_Union(..)) for performance unless you never have more than
 a few geometries.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4991#comment:11>
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