How to lag using dynamic offset in SQL AWS Athena?

I have a table with a column of numbers and then other columns with other data. I have created column "floor10" that has floor of those numbers as a multiple of 10 (e.g. 8 -> 0, 17 -> 10, etc.). What I'd like to do is create another column that has the lag of "floor10" and shows it for each row. There's no fixed number of rows per distinct value of "floor10" so I'm not sure how I would do this using LAG in SQL on AWS Athena.

For example,

I'd like something like,

The following did not work:

SELECT
Num,
floor10,
Name,
LAG(floor10) OVER (PARTITION BY Name, Num ORDER BY Name, Num) AS floor10_prev
FROM table

Alternatively, I tried making a subquery with distinct "floor10" and "Name" and then use lag on that before joining on the main table. While this got the desired result, this doesn't seem efficient and doing that on a much larger dataset took a long time to complete.

You can use dynamically calculate shift value for lag() - that is row number in group of rows with (name,num). See example

select *
  ,lag(floor10,rn)over(partition by name order by floor10) prev_fllor10
from(
   select *
     ,row_number()over(partition by name,floor10 order by floor10)rn
   from test
)a

fiddle

Test data