Name
ST_MemUnion — Aggregate function which unions geometries in a memory-efficent but slower way
Synopsis
geometry ST_MemUnion(geometry set geomfield);
Description
An aggregate function that unions the input geometries, merging them to produce a result geometry with no overlaps. The output may be a single geometry, a MultiGeometry, or a Geometry Collection.
![[Note]](../images/note.png)
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Produces the same result as ST_Union, but uses less memory and more processor time. This aggregate function works by unioning the geometries incrementally, as opposed to the ST_Union aggregate which first accumulates an array and then unions the contents using a fast algorithm. |
This function supports 3d and will not drop the z-index.
However, the result is computed using XY only.
The result Z values are copied, averaged or interpolated.
Examples
SELECT id,
ST_MemUnion(geom) as singlegeom
FROM sometable f
GROUP BY id;