oracle sql query statement NVL not working as desired -


i trying learn oracle sql , below query. wanted print everyone's manager , if doesn't manager should return "no one".

problem: getting blank statement instead of "no one". help?

select nvl(m.first_name || ' '     || m.last_name, 'no one') || ' supervises '     || w.first_name || ' ' || w.last_name   employees w, employees m  w.manager_id = m.employee_id(+);  nvl(m.first_name||''||m.last_name,'noone')||'supervise ------------------------------------------------------ james smith supervises ron johnson ron johnson supervises susan jones ron johnson supervises fred hobbs   supervises james smith

this because of reason, when m.first_name , m.last_name null manager, m.first_name || ' ' || m.last_name not result in null, ' '. so, print space instead of 'no one'. can achieve desired results using nvl2 

select nvl2( m.first_name ||m.last_name , m.first_name || ' ' || m.last_name, 'no one' )    || ' supervises '    || w.first_name    || ' '    || w.last_name employees w, employees m w.manager_id = m.employee_id(+);

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