Select 10 percent for each group for the previous month - sql

Question

I can get the top 10 percent for the previous month using
select top 10 percent ID, Ref, Entered_Date, [Type], CREATEDBY, Office, Created_Date, Amt from Tbl
where DATEPART(m, Entered_Date) = DATEPART(m, DATEADD(m, -1, getdate())) AND DATEPART(yyyy, Entered_Date) = DATEPART(yyyy, DATEADD(m, -1, getdate())) and
CreatedBy ='User1')
order by amt DESC
I am having to do this many times for each user using a union, how can I do this on one query? When I add the other users CreatedBy in('User1','User2') it doesn't work. I had a look at row over partition but cant figure it out. I'm using SSMS 2017.
Updated with below
Select * From(
select ID, Ref, Entered_Date, [Type], CREATEDBY, Office, Created_Date, Amt
NTILE (10) OVER ( PARTITION BY CREATEDBY ORDER BY Amt desc) AS PercentageNo
from Tbl
where DATEPART(m, Entered_Date) = DATEPART(m, DATEADD(m, -1, getdate())) AND DATEPART(yyyy, Entered_Date) = DATEPART(yyyy, DATEADD(m, -1, getdate()))
/*Entered_Date between DATEADD(m, -2, getdate()) and DATEADD(m, -1, getdate()) */ )as SubQuery
where PercentageNo=1 order By Amt

Answer 1

you can use GROUP BY for select percentage of each user as this:
select top 10 percent ID, Ref, Entered_Date, [Type], CREATEDBY, Office, Created_Date, Amt
FROM Tbl
where DATEPART(m, Entered_Date) = DATEPART(m, DATEADD(m, -1, getdate()))
AND DATEPART(yyyy, Entered_Date) = DATEPART(yyyy, DATEADD(m, -1, getdate()))
AND CreatedBy IN ('User1','User2')
GROUP BY ID, Ref, Entered_Date, [Type], CREATEDBY, Office, Created_Date, Amt
order by amt DESC

Answer 2

you can use row_number() for this reason

Answer 3

If you want the top 10% for each user, I would recommend using logic such as this:
select ID, Ref, Entered_Date, [Type], CREATEDBY, Office, Created_Date, Amt
from (select t.*,
row_number() over (partition by user order by amt desc) as seqnum,
count(*) over (partition by user) as cnt
from Tbl t
where Entered_Date >= dateadd(month, -1, dateadd(day, 1 - day(getdate()), convert(date, getdate()))) and
Entered_Date < dateadd(day, 1 - day(getdate()), convert(date, getdate()))
) t
where seqnum <= cnt / 10;
order by user, amt desc;
Note the change to the date arithmetic. The functions are all applied only on getdate(). This allows indexes to be used to winnow down the data.
The key for solving your problem is using window functions with the partition by user construct to do separate counts and enumerations for each user.

Answer 4

This I now woking as expected thanks to Gordon Linoff Re Dates and Caius Jard for pointing me in to Ntile
Select * From(
select ID, Ref, Entered_Date, [Type], CREATEDBY, Office, Created_Date, Amt
NTILE (10) OVER ( PARTITION BY CREATEDBY ORDER BY Amt desc) AS PercentageNo
from Tbl
where Entered_Date >= dateadd(month, -1, dateadd(day, 1 - day(getdate()), convert(date, getdate()))) and Entered_Date < dateadd(day, 1 - day(getdate()), convert(date, getdate())) as SubQuery where PercentageNo=1 order By Amt