[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 mdavis):

 Hoo boy there's a lot of confusion going on here. Some of it is due to
 slightly confusing or possibly erroneous documentation, and some is due to
 (apparently) inconsistent implementation.

 The key fact is that it is intentional that Union operation semantics
 cause *all* lines to be nodedd, even single ones.  The input line in this
 case crosses itself, so it is turned into a MultiLineString.

 Given this, it seems like `ST_MemUnion` may have an optimization that
 avoids this semantic - which should probably be fixed, so things are
 consistent.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/4991#comment:4>
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