SQL Server 2022

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create table TableA (
  Target int, 
  Agent varchar(20), 
  Ranka int
)

insert into TableA values
(15000, 'A', null),
(15000, 'A', null),
(14500, 'A', null);

3 rows affected

with cte as (
  select Target, Agent, rank() over (partition by Agent order by Target desc) as Ranka
  from TableA
)
select Target, Agent, cast(Ranka as float)/CAST(count(*) over (partition by Agent) AS FLOAT)*100 as Percentile
from cte


Target
Agent
Percentile


15000
A
33.3333333333333

15000
A
33.3333333333333

14500
A
100


select Target, Agent, rank() over (partition by Agent order by Target desc) as Ranka
from TableA


Target
Agent
Ranka


15000
A
1

15000
A
1

14500
A
3