Find min and max for subsets of consecutive rows – gaps and islands

You want to find consecutive groups of similar rows and then aggregation. I like the difference of row numbers approach:

select name, act, min(startt) as startt, max(endd) as endd
from (select i.*,
             row_number() over (partition by name, act order by rn) as seqnum_na,
             row_number() over (partition by name order by rn) as seqnum_n
      from input i
     ) i
group by (seqnum_n - seqnum_na), name, act;

You can see how this works by looking at what the subquery does.