Rank in SQL special case

Write Hive SQL query to get the output from the input shown below.
I am trying to add rank column which is ordered by event_ts. But if there is same item_id for any consecutive rows, they should get the same rank. Partition by item_id will not work here as it will rank each partition window starting from 1. But I want the rank to monotonically increase.

NOTE: dense_rank() will not solve this

Input:

Output:

This should give you what you're looking for. It will keep the same rank if the row above has the same value, then will continue incrementally ranking.

Select
event_ts,
item_id,
sum(inc) over(order by event_ts) as rank_order
from (
  select *,
    case when lag(item_id) over (order by event_ts) = item_id
      then 0 else 1 end as inc   
  from table1
) table2

table1

Results