ST_MemUnion
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## 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.

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;

## See Also

ST_Union

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