# ST_NumInteriorRing function

the ST_NumInteriorRing function takes a polygon as an input parameter and returns the number of its interior rings.

If the given polygon is null or is empty, then null is returned.

If the polygon has no interior rings, then 0 (zero) is returned.

This function can also be called as a method.

## Syntax

## Parameter

- polygon
- A value of type ST_Polygon that represents the polygon for which the number of interior rings is returned.

## Return type

INTEGER

## Example

The following example creates two
polygons:

- One with two interior rings
- One without any interior rings

```
SET CURRENT FUNCTION PATH = CURRENT FUNCTION PATH, db2gse
CREATE TABLE sample_polys (id INTEGER, geometry ST_Polygon)
INSERT INTO sample_polys
VALUES (1, 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 sample_polys
VALUES (2, ST_Polygon('polygon ((5 15, 50 15, 50 105, 5 15))' , 0) )
```

The ST_NumInteriorRing function is used to return
the number of rings in the geometries in the table:

```
SELECT id, ST_NumInteriorRing(geometry) NUM_RINGS
FROM sample_polys
```

Results: ```
ID NUM_RINGS
---------- ---------------
1 2
2 0
```