Вы можете использовать row_number()
:
select
row_number() over(partition by EmployeeId order by PaycheckDate) week,
EmployeeId,
PaycheckDate,
Amount
from mytable
order by week, EmployeeId
Если вы хотите только первые 13 недель на сотрудника, то:
select *
from (
select
row_number() over(partition by EmployeeId order by PaycheckDate) week,
EmployeeId,
PaycheckDate,
Amount
from mytable
) t
where week <= 13
order by week, EmployeeId