Calculate average multilinestring point elevation

Question

I'm triying to calculate the average elevation of some multilinestring points.

Is there a fastest way than this pgsql function?

CREATE OR REPLACE FUNCTION topstation.sig_moyenne_z(ingeom geometry)
  RETURNS double precision AS
$BODY$
DECLARE 
    geom2 geometry;
    sum double precision;
    max double precision;
BEGIN       
    sum:=0;
    geom2=ST_LineMerge(inGeom);
    max:=ST_NPoints(geom2);
    IF max > 1 THEN

    FOR i IN 1..max
    LOOP
        sum := sum + ST_Z(ST_PointN(geom2,i));
    END LOOP;
    RETURN sum / max;
     ELSE
    return 9999;
     END IF;
END;
$BODY$
  LANGUAGE plpgsql IMMUTABLE
  COST 100;

Answer 1

Maybe

Select avg(z_val) from 
(select st_z((st_dumppoints(geom)).geom) z_val from the_table) a