Updating table using row_number() over (order by columnName)

--Create temp table
create table #temptable
(
col1 int,
col2 int,
col3 int
)
--insert three values
insert into #tempTable values (1,2,3)
insert into #tempTable values (1,2,3)
insert into #tempTable values (1,2,3)
--update value based on row_number() over (order by columnName)
update temp
set col3=3
from
(
select row_number() over(order by col1) as row_id,* from #tempTable
)temp
where row_id =2
--View Updated Data
select * from #tempTable