You mean something like this?
select * from (
select department_id,
first_name, last_name, salary,
round(avg(salary) over (partition by department_id)) avg_sal,
min(salary) over (partition by department_id) min_sal
from hr.employees
)
where salary = min_sal
order by 1, 2;
DEPARTMENT_ID FIRST_NAME LAST_NAME SALARY AVG_SAL MIN_SAL
10 Jennifer Whalen 4,400 4,400 4,400
20 Pat Fay 6,000 9,500 6,000
30 Karen Colmenares 2,500 4,150 2,500
40 Susan Mavris 6,500 6,500 6,500
50 TJ Olson 2,100 3,476 2,100
60 Diana Lorentz 4,200 5,760 4,200
70 Hermann Baer 10,000 10,000 10,000
80 Sundita Kumar 6,100 8,956 6,100
90 Lex De Haan 17,000 19,333 17,000
90 Neena Kochhar 17,000 19,333 17,000
100 Luis Popp 6,900 8,601 6,900
110 William Gietz 8,300 10,154 8,300
Kimberely Grant 7,000 7,000 7,000