ST_IsRing() method

Tests if the ST_Curve value is a ring. A curve is a ring if it is closed and simple (no self intersections).

Syntax

curve-expression.ST_IsRing()

BIT Returns 1 if the curve is a ring (and non empty). Otherwise, returns 0.

Example 1 – The following returns all rows in SpatialShapes containing rings. The IF expression is required to ensure the TREAT function is not executed if the Shape is not a subtype of ST_Curve. Without the IF expression the server may reorder the conditions in the WHERE clause, leading to an error.
```
SELECT * FROM SpatialShapes
WHERE IF Shape IS OF ( ST_Curve )
AND TREAT( Shape AS ST_Curve ).ST_IsRing() = 1 THEN 1 ENDIF = 1
```
The following returns all rows in curve_table that have geometries that are rings. This example assumes the geometry column has type ST_Curve, ST_LineString, ST_CircularString or ST_CompoundCurve.
```
SELECT * FROM curve_table WHERE geometry.ST_IsRing() = 1
```

SQL/MM (ISO/IEC 13249-3: 2006) 7.1.6