[postgis-users] Make Union between 2 layers

[Alain Benard]

Hi,
I would like to make an operation between two tables with geometry 
(polygon) - user's GIS call this operation a UNION.

I think this :

  * Step1 : make st_intersection (where st_intersects) and obtains the 4
    little square with attributes from the two table. I call the result
    layerintersect
  * Step 2 : make a unique polygon with the layerintersect (Step 1)
  * Step 3 : use this polygon  with the two table and st_difference
  * assembly the 3 result (layerintersect + the 2 difference) with a
    classic union (SQL)

The second step make a big polygon and for other data it can be a problem ??
Is there another way to make this job?
Thanks in advance.

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