Database Reference
In-Depth Information
How it works...
Youhavebeenusingthe ST_Union PostGISfunctiontomakeapolygonmergeon
a common attribute. This function can be used as an aggregate PostgreSQL func-
tion (such as SUM , COUNT , MIN , and MAX ) on the layer's geometric field, using the
common attribute in the GROUP BY clause.
Note that ST_Union can also be used as a nonaggregate function to perform the
union of two geometries (which are the two input parameters).
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