Calculate percentage based on row_number in sql - sql-server

Question

I'm trying to write a sql query that for each returned row, will also return a percentage (0-100) based on its row position. To further complicate this, the query is also currently grouped. Here's some example data to play with:
create table #test(StockId int)
insert into #test values (101), (101), (202), (202), (303), (404), (505)
select
StockId,
count(*) as BinMovements
from #test
group by StockId
order by BinMovements desc
This query currently returns:
StockId, BinMovements
101, 2
202, 2
303, 1
404, 1
505, 1
(Though obviously, because BinMovements is either 2 or 1 it would be equally correct to return the StockIds in a different order such as):
202, 2
101, 2
404, 1
303, 1
505, 1
I'd like to add a 'percentage' column, but this is really just based on row position, so I'd like to see values like:
101, 2, 100
202, 2, 80
303, 1, 60
404, 1, 40
505, 1, 20
I imagine the solution may involve ROW_NUMBER, and I started down this path thinking I could just get ROW_NUMBER / total rows * 100, but this isn't working for some reason. Possibly because of the group by clause?
select
StockId,
count(*) as BinMovements,
ROW_NUMBER() OVER(order by (count(*))) as RowNumber,
count(*) over () as TotalCount,
(ROW_NUMBER() OVER(order by (count(*)))) / (count(*) over ()) * 100 as Percentage
from #test
group by StockId
order by RowNumber desc
returns:
StockId BinMovements RowNumber TotalCount Percentage
202 2 5 5 100
101 2 4 5 0
505 1 3 5 0
404 1 2 5 0
303 1 1 5 0
I'd prefer to do this in a single select if possible, though if not wrapping it in an outer select may be a solution. Thanks

Answer 1

Both COUNT and ROW_NUMBER functions returns BIGINT.
Therefore result of division is also converted to BIGINT.
This works (you should multiply before divide):
(ROW_NUMBER() OVER(order by (count(*)))) * 100 / (count(*) over ()) as Percentage

Answer 2

Using count() over() and row_number() similar to your question, just reordering equation.
Note that the order by for the row_number() is the inverse of the order by for the statement, because we want to start the percentage at 100. Otherwise you can end up with 80 as the first row, 100 as the second, etc.
select
StockId
, BinMovements = count(*)
, Percentage = 100/count(*) over ()
* row_number() over (order by count(*) asc, stockid desc)
from #test
group by StockId
order by BinMovements desc, StockId asc
rextester demo: http://rextester.com/TCPE10348
+---------+--------------+------------+
| StockId | BinMovements | Percentage |
+---------+--------------+------------+
| 101 | 2 | 100 |
| 202 | 2 | 80 |
| 303 | 1 | 60 |
| 404 | 1 | 40 |
| 505 | 1 | 20 |
+---------+--------------+------------+
If you want a decimal percentage, change 100 to 100.0 in the equation.