# ST\_NumInteriorRings

## Syntax

```sql
ST_NumInteriorRings(poly)
NumInteriorRings(poly)
```

## Description

Returns an integer containing the number of interior rings in the Polygon value `poly`.

Note that according the OpenGIS standard, a [POLYGON](https://mariadb.com/docs/server/reference/sql-statements/geometry-constructors/geometry-constructors/polygon) should have exactly one ExteriorRing and all other rings should lie within that ExteriorRing and thus be the InteriorRings. Practically, however, some systems, including MariaDB's, permit polygons to have several 'ExteriorRings'. In the case of there being multiple, non-overlapping exterior rings ST\_NumInteriorRings() will return `1`.

`ST_NumInteriorRings()` and `NumInteriorRings()` are synonyms.

## Examples

```sql
SET @poly = 'Polygon((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1))';

SELECT NumInteriorRings(GeomFromText(@poly));
+---------------------------------------+
| NumInteriorRings(GeomFromText(@poly)) |
+---------------------------------------+
|                                     1 |
+---------------------------------------+
```

Non-overlapping 'polygon':

```sql
SELECT ST_NumInteriorRings(ST_PolyFromText('POLYGON((0 0,10 0,10 10,0 10,0 0),
  (-1 -1,-5 -1,-5 -5,-1 -5,-1 -1))')) AS NumInteriorRings;
+------------------+
| NumInteriorRings |
+------------------+
|                1 |
+------------------+
```

<sub>*This page is licensed: GPLv2, originally from*</sub> [<sub>*fill\_help\_tables.sql*</sub>](https://github.com/MariaDB/server/blob/main/scripts/fill_help_tables.sql)

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