Объединение диапазонов одним запросом с моделькой

или Забавы с модельками - 2

На очередное коротенькое баловство вдохновил этот вопрос
Скрипт обновлен, т.к. предыдущий был не оптимальным. Данный вариант лучший среди вариантов с решениями с моделью:

select a, max(b) from (
    select a,b
    from t
    model
         return all rows
         dimension by (row_number() over(order by a,b) rn)
         measures(a,
                 greatest(b,
                          nvl(max(b) over(order by a asc,b desc rows between unbounded preceding and 1 preceding),b)
                 ) b)
         rules (
            a[any]= case when a[cv()] <= b[cv()-1]+1
                     then a[cv()-1]
                     else a[cv()]
                    end
         )
)
group by a;

А теперь наиболее быстрый вариант - вариант на аналитике:

select * from (
    select 
         nvl(sg,lag(sg) over(order by nvl(sg,eg))) sg,
         eg
    from (
         select 
             a,
             b,
             case 
                when 
                 a-1>max(b) over(order by a asc,b desc rows between unbounded preceding and 1 preceding)
                 or max(b) over(order by a asc,b desc rows between unbounded preceding and 1 preceding) is null
                then a
             end sg,
             case 
                when 
                 (
                 lead(a) over(order by a asc,b desc)
                 >
                 1+max(b) over(order by a asc,b desc rows between unbounded preceding and current row)
                 )
                 or lead(a) over(order by a asc,b desc) is null
                then max(b) over(order by a asc,b desc rows between unbounded preceding and current row)
             end eg
         from t
    )
    where sg is not null 
    or eg is not null
)where eg is not null