select 1 as myorderBy,name,salary from sometable where manager='Y'
UNION ALL
select 2 as myorderBy,name,salary from sometable where manager='N'
ORDER BY myorderBy,salary

select 
  CASE 
    WHEN manager='Y'
    THEN 1 
    ELSE 2
END 
as myorderBy,name,salary 
from sometable 
ORDER BY myorderBy,salary