wm_concat.sql

CREATE OR REPLACE FUNCTION wm_concat_finalfn(anyarray)
RETURNS text
LANGUAGE SQL
IMMUTABLE AS $$
    SELECT array_to_string($1, ',');
$$;

DROP AGGREGATE IF EXISTS wm_concat(anyelement);

CREATE AGGREGATE wm_concat(anyelement) (
    SFUNC = array_append,
    STYPE = anyarray,
    FINALFUNC = wm_concat_finalfn
);