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).