postgresql 增加字符串累加函数sumtext（转载)

CREATE OR REPLACE FUNCTION concat(character varying, character varying)
RETURNS character varying AS
$BODY$ 
DECLARE t varchar; 
BEGIN IF character_length($1) > 0 
THEN t = $1||','|| $2; 
ELSE  t = $2; 
END IF;
RETURN t;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
ALTER FUNCTION concat(character varying, character varying) OWNER TO postgres;
GRANT EXECUTE ON FUNCTION concat(character varying, character varying) TO public;
GRANT EXECUTE ON FUNCTION concat(character varying, character varying) TO postgres;

CREATE AGGREGATE sumtext(
BASETYPE=varchar,
SFUNC=concat,
STYPE=varchar);
ALTER AGGREGATE sumtext(varchar) OWNER TO postgres;