SQL Challenge/Quebra-cabeça:Como mesclar intervalos aninhados?

with l as ( select level lvl from dual connect by level < 66 ),
     r as ( select range_start r1, range_end r2, range_val v, 
                    range_end - range_start + 1 cnt 
              from ranges ),
     t1 as (select distinct lvl, 
                   nvl(max(v) keep (dense_rank first order by cnt) 
                              over (partition by lvl), '*' ) m
              from l left join r on lvl between r1 and r2 ),
     t2 as (select lvl, m, case when lag(m) over (order by lvl) <> m then 0 else 1 end mrk 
              from t1),
     t3 as (select lvl, m, lvl - sum(mrk) over (order by lvl) grp from t2)
select min(lvl) r1, max(lvl) r2, nullif(min(m), '*') val
  from t3 group by grp order by r1

• l - gerador de números,
• r - dados de ranges com distância contada,
• t1 - encontra valor com distância mínima para cada lvl,
• t2 - adiciona marcadores informando se o intervalo começa,
• t3 - adiciona a coluna que usaremos a seguir para agrupar dados.