Select avg salary from two depts, to compare??

Question

Greetings.. Need some help with a query..
Want to select the average salary of one dept, call it dept 400, compared to the avg salary of all other depts. Also want the count of employees in dept 400 vs the number of employees in all other depts.. and would like for all this to be in one select statement. All of this data can be extracted from a single table called employees..
Any and all help apprciated!!

Answer 1

with t as ( select 1 employee_id, 1 dept, 1000 salary from dual union all
            select 2 employee_id, 1 dept, 2000 salary from dual union all
            select 3 employee_id, 1 dept, 3000 salary from dual union all
            select 4 employee_id, 1 dept, 4000 salary from dual union all
            select 5 employee_id, 21 dept, 1500 salary from dual union all
            select 6 employee_id, 21 dept, 4500 salary from dual union all
            select 7 employee_id, 21 dept, 3000 salary from dual union all
            select 8 employee_id, 15 dept, 3000 salary from dual union all
            select 9 employee_id, 15 dept, 8000 salary from dual union all
            select 10 employee_id, 15 dept, 4000 salary from dual )
select dept, count(employee_id) emp_count, avg(salary) avg_salary
from t           
group by dept
DEPT     EMP_COUNT     AVG_SALARY
1     4     2500
21     3     3000
15     3     5000