ST_PolygonFromText-ApsaraDB RDS(RDS)-阿里云帮助中心

Constructs a polygon geometry from a Well-Known Text (WKT) string and an optional spatial reference identifier (SRID).

If you know the WKT string represents a polygon, use ST_GeomFromText instead. ST_GeomFromText is faster because no unnecessary checks are required.

Syntax

geometry ST_PolygonFromText(text wKT);
geometry ST_PolygonFromText(text wKT, integer srid);

Parameters

Parameter	Type	Description
`wKT`	text	The WKT string representing the polygon.
`srid`	integer	The SRID of the polygon. Defaults to `0` if not specified.

Return behavior

Returns a geometry object if the WKT string represents a valid polygon.
Returns NULL if the WKT string does not represent a polygon (for example, a POINT or LINESTRING).

Examples

Construct a polygon with SRID 4326:

SELECT ST_AsEWKT(ST_PolygonFromText('POLYGON((1 2,3 4,5 6,1 2))', 4326));
              st_asewkt
--------------------------------------
 SRID=4326;POLYGON((1 2,3 4,5 6,1 2))
(1 row)