Hi,
I notice your polygon has many repeated vertex in same points.
I suggest you to remove they,
using
ST_RemoveRepeatedPoints()
ST_RemoveRepeatedPoints(
ST_GeomFromEWKT('SRID=3003;
POLYGON((
168119.443682473 451093.811197312,
197555.469699649 451093.811197312,
197555.469699649 437539.54805452,
168119.443682473 437539.54805452,
168119.443682473 437539.54805452,
168119.443682473 451093.811197312
))')) as geom;
I guess they could do some trouble in ST_Difference.
Regards,
Andrea.
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