Oracle - Convert value from rows into ranges

Question

Are there any techniques that would allow a row set like this

WITH 
base AS
(
    SELECT  1 N FROM DUAL UNION ALL
    SELECT  2 N FROM DUAL UNION ALL
    SEL         


        

Answer 1

Another way:

WITH base AS  
(
    SELECT  1 N FROM DUAL UNION ALL
    SELECT  2 N FROM DUAL UNION ALL
    SELECT  3 N FROM DUAL UNION ALL
    SELECT  6 N FROM DUAL UNION ALL
    SELECT  7 N FROM DUAL UNION ALL
    SELECT 17 N FROM DUAL UNION ALL
    SELECT 18 N FROM DUAL UNION ALL
    SELECT 19 N FROM DUAL UNION ALL
    SELECT 21 N FROM DUAL
)
select min(n), max(n) from 
  (
    select n, connect_by_root n root from base
    connect by prior n = n-1
    start with n not in (select n from base b 
                         where exists (select 1 from base b1 where b1.n = b.n-1)
                        )
  ) 
  group by root
  order by root