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\_ExteriorRing
<a name="ST_ExteriorRing-function"></a>

ST\_ExteriorRing returns a closed linestring that represents the exterior ring of an input polygon. The dimension of the returned geometry is the same as that of the input geometry.

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

```
ST_ExteriorRing(geom)
```

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

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

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

`GEOMETRY` of subtype `LINESTRING`. 

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

If *geom* is null, then null is returned. 

If *geom* is not a polygon, then null is returned. 

If *geom* is empty, then an empty polygon is returned. 

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

The following SQL returns the exterior ring of a polygon as a closed linestring. 

```
SELECT ST_AsEWKT(ST_ExteriorRing(ST_GeomFromText('POLYGON((7 9,8 7,11 6,15 8,16 6,17 7,17 10,18 12,17 14,15 15,11 15,10 13,9 12,7 9),(9 9,10 10,11 11,11 10,10 8,9 9),(12 14,15 14,13 11,12 14))')));
```

```
st_asewkt
-----------
 LINESTRING(7 9,8 7,11 6,15 8,16 6,17 7,17 10,18 12,17 14,15 15,11 15,10 13,9 12,7 9)
```