GIS: IsRing returns false for a primitive triangle

MariaDB [test]> select ST_IsRing(ST_LineFromText('LINESTRING(0 0,0 10,10 10,0 0)'));

+--------------------------------------------------------------+

| ST_IsRing(ST_LineFromText('LINESTRING(0 0,0 10,10 10,0 0)')) |

+--------------------------------------------------------------+

|                                                            0 |

+--------------------------------------------------------------+

pgis=# select ST_IsRing(ST_LineFromText('LINESTRING(0 0,0 10,10 10,0 0)'));

 st_isring 

-----------

 t

(1 row)