select specific column from subquery

Question

My sample data with the Emp table

Emp

deptno eno
1       1
1       2
1       3
2       1
2       2

output:

deptno  eno
1        3
2        2

out of this i need to have only one column in final output only

deptno
1
2

I am trying to write

select deptno from emp where deptno in (select deptno,max(eno)
from emp
group by deptno);

It is throwing error

Answer 1

I'm thinking . . .

select distinct deptno
from emp;

Does that meet your needs?

Answer 2

Try this

select deptno from emp where deptno in (
    select deptno from emp where eno in (
        select MAX(eno) from emp))

Answer 3

select deptno
from emp 
group by deptno