text: 
  /* 
   mysqlcompat-1.0b3
   public domain
   GROUP_CONCAT()
   Note: For DISTINCT and ORDER BY a subquery is required
  */
  
  CREATE OR REPLACE FUNCTION _group_concat(text, text)
  RETURNS text AS $$
    SELECT CASE
      WHEN $2 IS NULL THEN $1
      WHEN $1 IS NULL THEN $2
      ELSE $1 operator(pg_catalog.||) ' ' operator(pg_catalog.||) $2
    END
  $$ IMMUTABLE LANGUAGE SQL;
  
  DROP AGGREGATE IF EXISTS group_concat(text);
  
  CREATE AGGREGATE group_concat (
  	BASETYPE = text,
  	SFUNC = _group_concat,
  	STYPE = text
  );
  
  