How can I find duplicate consecutive values in this table?

Question

Say I have a table which I query like so:

select date, value from mytable order by date

and this gives me results:

date             


        

Answer 1

This is a simplified version of @Bob Jarvis' answer, the main difference being the use of just one subquery instead of four,

with f as (select row_number() over(order by d) rn, d, v from t3)
select
  a.d, a.v,
  case when a.v in (prev.v, next.v) then '*' end match
from
  f a
    left join
  f prev
    on a.rn = prev.rn + 1
    left join
  f next
    on a.rn = next.rn - 1
order by a.d
;