PostgreSQL - Error extraño en función

CREATE OR REPLACE FUNCTION dias_sin()

 RETURNS int AS $$

DECLARE

 	diferencia INT;

	contador int := 1;

BEGIN

     while contador < (select salida_num from datos order by salida_num desc limit 1) loop

      SELECT max(DT2.FECHA::DATE - DT1.FECHA::DATE) INTO  diferencia

      FROM DATOS DT1, DATOS DT2  WHERE DT1.SALIDA_NUM = DT2.SALIDA_NUM + 1

    	end loop;

    RETURN COALESCE(diferencia,0);

end;

$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION dias_sin()

    RETURNS int AS

$$

DECLARE

 	diferencia INT;

	contador int := 1;

BEGIN

    WHILE contador < (SELECT salida_num FROM datos ORDER BY salida_num DESC LIMIT 1)

    LOOP

        SELECT MAX(DT2.FECHA::DATE - DT1.FECHA::DATE) INTO  diferencia

        FROM DATOS DT1, DATOS DT2

        WHERE DT1.SALIDA_NUM = DT2.SALIDA_NUM + 1;

    END LOOP;

    RETURN COALESCE(diferencia,0);

END;

$$

LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION dias_sin()

 RETURNS integer

 LANGUAGE plpgsql

AS $function$

DECLARE

 	days int;

BEGIN

     WITH dias AS (

	SELECT

	    t.id,

	    t.fecha - LAG(t.fecha,1) OVER(PARTITION BY t.id ORDER BY t.fecha) diff

	FROM (SELECT 1 id, fecha::date fecha

		FROM datos ORDER BY fecha::date) t)

SELECT MAX(d.diff) INTO days

FROM dias d;

RETURN days;

end;

$function$

;