with t1 as ( select distinct name, 
        row_number() over (order by name) id
            from occupations
            where lower(occupation) = 'doctor'
            ),
t2 as  ( select distinct name, 
        row_number() over (order by name) id
            from occupations
            where lower(occupation) = 'professor'
            ),  
t3 as  ( select distinct name, 
        row_number() over (order by name) id
            from occupations
            where lower(occupation) = 'singer'
            ),  
t4 as  ( select distinct name, 
        row_number() over (order by name) id
            from occupations
            where lower(occupation) = 'actor'
            )
select distinct t1.name, t2.name, t3.name, t4.name
from t1
full outer join t2
on t1.id = t2.id
full outer join t3
on t2.id = t3.id
full outer join t4
on t3.id = t4.id
order by 1, 2, 3, 4;