SQL Challenge/Puzzle: How to merge nested ranges?

Question

• This challenge is based on a real life use-case involving IP ranges.
• The solution I came with is based on the stack trace challenge I\'ve presented previously

Answer 1

Oracle solution:

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

Output is as requested. My English is far from good, so it's hard to explain, but let's try:

• l - number generator,
• r - data from ranges with counted distance,
• t1 - finds value with minimal distance for each lvl,
• t2 - adds markers telling if range starts,
• t3 - adds column which we will next use for grouping data.