ST_Multi — Returns the geometry as a MULTI* geometry. If the geometry is already a MULTI*, it is returned unchanged.
geometry ST_Multi(geometry g1);
Returns the geometry as a MULTI* geometry. If the geometry is already a MULTI*, it is returned unchanged.
SELECT ST_AsText(ST_Multi(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,
743265 2967450,743265.625 2967416,743238 2967416))')));
st_astext
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MULTIPOLYGON(((743238 2967416,743238 2967450,743265 2967450,743265.625 2967416,
743238 2967416)))
(1 row)