GEOMETRY ST_RemoveDuplicatedCoordinates(GEOMETRY geom);

SELECT ST_RemoveDuplicatedCoordinates('
             MULTIPOINT((4 4), (1 1), (1 0), (0 3), (4 4))');
-- Answer:   MULTIPOINT ((4 4), (1 1), (1 0), (0 3)) 

SELECT ST_RemoveDuplicatedCoordinates('
             MULTIPOINT((4 4), (1 1), (1 0), (1 1), (4 4), (0 3), (4 4))');
-- Answer:   MULTIPOINT ((4 4), (1 1), (1 0), (0 3))

SELECT ST_RemoveDuplicatedCoordinates('
             LINESTRING(4 4, 1 1, 1 1)');
-- Answer:   LINESTRING (4 4, 1 1)  

SELECT ST_RemoveDuplicatedCoordinates('
             POLYGON((4 4, 1 1, 1 1, 0 0, 4 4))');
-- Answer:   POLYGON ((4 4, 1 1, 0 0, 4 4)) 

SELECT ST_RemoveDuplicatedCoordinates(
        'GEOMETRYCOLLECTION(
             POLYGON((1 2, 4 2, 4 6, 1 6, 1 6, 1 2)),
             MULTIPOINT((4 4), (1 1), (1 0), (1 1)))');
-- Answer: GEOMETRYCOLLECTION (
--           POLYGON ((1 2, 4 2, 4 6, 1 6, 1 2)), 
--           MULTIPOINT ((4 4), (1 1), (1 0)))