with t as 
(
select 'A' as product,1 as sno from dual union all
select 'A',2 from dual union all
select 'A',4 from dual union all
select 'B',3 from dual union all
select 'B',5 from dual union all
select 'B',6 from dual 
)
select product, listagg(sno,',') within group(order by rn) sno
from
(
select product, decode(min(sno),max(sno),min(sno),min(sno)||'-'||max(sno)) sno, min(rn) rn
from
(
select product, to_char(sno) sno, row_number() over(partition by product order by sno) rn 
from t
)
group by product, rn - sno
)
group by product

SELECT product
     , LISTAGG(DECODE(x, sno, '-', '', '', ',') || sno) WITHIN GROUP(ORDER BY sno) x
  FROM (SELECT product, sno
             , LAG (sno) OVER(PARTITION BY product ORDER BY sno) + 1 x
             , LEAD(sno) OVER(PARTITION BY product ORDER BY sno) - 1 y
          FROM t
        )
 WHERE LNNVL(x = y)
 GROUP BY product
;

LNNVL이 이렇게 사용될 줄이야0-0