# ST_NumInteriorRing

Release 9.3
Note: This topic was updated for 9.3.1.

## Definition

ST_NumInteriorRing takes an ST_Polygon and returns the number of its interior rings.

## Syntax

Oracle

``sde.st_numinteriorring (pl1 sde.st_geometry)``

PostgreSQL

``st_numinteriorring (pl1 st_geometry)``

Integer

## Example

An ornithologist wants to study a bird population on several South Seas islands. She wants to identify which islands contain one or more lakes because the bird species she is interested in feeds only in freshwater lakes.

The ID and name columns of the islands table identify each island, while the land ST_Polygon column stores the islands' geometry.

Oracle

``````CREATE TABLE islands (id integer,
name varchar(32),
land sde.st_geometry);
INSERT INTO islands VALUES (
1,
'Bear',
sde.st_polygon ('polygon ((40 120, 90 120, 90 150, 40 150, 40 120),(50 130, 60 130, 60 140, 50 140, 50 130),(70 130, 80 130, 80 140, 70 140, 70 130))', 0)
);
INSERT INTO islands VALUES (
2,
'Johnson',
sde.st_polygon ('polygon ((10 10, 50 10, 10 30, 10 10))', 0)
);``````

PostgreSQL

``````CREATE TABLE islands (id integer,
name varchar(32),
land st_geometry);
INSERT INTO islands VALUES (
1,
'Bear',
st_polygon ('polygon ((40 120, 90 120, 90 150, 40 150, 40 120),(50 130, 60 130, 60 140, 50 140, 50 130),(70 130, 80 130, 80 140, 70 140, 70 130))', 0)
);
INSERT INTO islands VALUES (
2,
'Johnson',
st_polygon ('polygon ((10 10, 50 10, 10 30, 10 10))', 0)
);``````

Because interior rings represent the lakes, the ST_NumInteriorRing function lists only those islands that have at least one interior ring.

Oracle

``````SELECT name
FROM islands
WHERE sde.st_numinteriorring (land)> 0;
NAME
Bear``````

PostgreSQL

``````SELECT name
FROM islands
WHERE st_numinteriorring (land)> 0;
name
Bear``````