If you want the 5 top employee ordered by salary

select * from (
select * from employee
order by salary desc
)
where rownum<=5


If you want all employees having the 5 top salaries

select * from employee
where salary in
(select salary from (
select distinct salary from employee
order by salary desc)
where rownum<=5)

OR

select * from (
select e.*,
dense_rank() over (order by salary desc) as dr
from employee e
)
where dr <=5