select e.emp_no,first_name,last_name,btype,salary,
case when btype=1 then salary*0.1 
     when btype=2 then salary*0.2 
     else salary*0.3 
end as bonus
from employees as e join salaries  as s on e.emp_no=s.emp_no and s.to_date='9999-01-01'
 join emp_bonus as eb on e.emp_no=eb.emp_no;

做一个表的自连接，因为要求不排序，保持原表的顺序。