ST_PolygonFromText — Makes a Geometry from WKT with the given SRID. If SRID is not given, it defaults to 0.
geometry ST_PolygonFromText(text  WKT);
geometry ST_PolygonFromText(text  WKT, integer  srid);
Makes a Geometry from WKT with the given SRID. If SRID is not given, it defaults to 0. Returns null if WKT is not a polygon.
OGC SPEC 3.2.6.2 - option SRID is from the conformance suite
                 
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                 If you are absolutely sure all your WKT geometries are polygons, don't use this function. It is slower than ST_GeomFromText since it adds an additional validation step.  | 
            
            
            This method implements the OGC Simple Features
            Implementation Specification for SQL 1.1.
         s3.2.6.2
            
            This method implements the SQL/MM specification.
         SQL-MM 3: 8.3.6
SELECT ST_PolygonFromText('POLYGON((-71.1776585052917 42.3902909739571,-71.1776820268866 42.3903701743239,
-71.1776063012595 42.3903825660754,-71.1775826583081 42.3903033653531,-71.1776585052917 42.3902909739571))');
st_polygonfromtext
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010300000001000000050000006...
SELECT ST_PolygonFromText('POINT(1 2)') IS NULL as point_is_notpoly;
point_is_not_poly
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t