Amazon Redshift will no longer support the creation of new Python UDFs starting Patch 198. Existing Python UDFs will continue to function until June 30, 2026. For more information, 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/). 

# ST\$1ExteriorRing
<a name="ST_ExteriorRing-function"></a>

ST\$1ExteriorRing 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)
```