Amazon Redshift will no longer support the use of Python UDFs after June 30, 2026. We will start enforcing it in phases. For more information on the details of Python end of life and migration options, see the [ blog post ](https://aws.amazon.com/blogs/big-data/amazon-redshift-python-user-defined-functions-will-reach-end-of-support-after-june-30-2026/) that was published on June 30, 2025. 

# ST\_Union
<a name="ST_Union-function"></a>

ST\_Union returns a geometry representing the union of two geometries. That is, it merges the input geometries to produce a resulting geometry with no overlaps. 

## Syntax
<a name="ST_Union-function-syntax"></a>

```
ST_Union(geom1, geom2)
```

## Arguments
<a name="ST_Union-function-arguments"></a>

 *geom1*   
A value of data type `GEOMETRY` or an expression that evaluates to a `GEOMETRY` type. 

 *geom2*   
A value of data type `GEOMETRY` or an expression that evaluates to a `GEOMETRY` type. 

## Return type
<a name="ST_Union-function-return"></a>

`GEOMETRY`

The spatial reference system identifier (SRID) value of the returned geometry is the SRID value of the input geometries.

If *geom1* or *geom2* is null, then null is returned. 

If *geom1* or *geom2* are empty, then an empty geometry is returned. 

If *geom1* and *geom2* don't have the same value for the spatial reference system identifier (SRID), then an error is returned. 

If *geom1* or *geom2* is a geometry collection, linestring, or multilinestring, then an error is returned. 

If *geom1* or *geom2* is not a two-dimensional (2D) geometry, then an error is returned. 

## Examples
<a name="ST_Union-function-examples"></a>

The following SQL returns the non-empty geometry representing the union of two input geometries. 

```
SELECT ST_AsEWKT(ST_Union(ST_GeomFromText('POLYGON((0 0,100 100,0 200,0 0))'), ST_GeomFromText('POLYGON((0 0,10 0,0 10,0 0))')));
```

```
        st_asewkt        
-------------------------
 POLYGON((0 0,0 200,100 100,5 5,10 0,0 0))
```