select c.*,
d.salary,
case when c.btype=1 then round(d.salary*0.1,1) 
     when c.btype=2 then round(d.salary*0.2,1) 
     else round(d.salary*0.3,1) end bonus
from
(
select a.emp_no,a.first_name,a.last_name,b.btype 
from employees a inner join emp_bonus b 
on a.emp_no=b.emp_no
)c
inner join
(
select * from salaries
where to_date='9999-01-01'
) d
on c.emp_no=d.emp_no
order by c.emp_no