帮忙写一条SQL语句

Question

两个表，表一employees  字段：employees_id， employees_name， salay，  department_id  其中employees_id是主键，department_id是外键
表二 department 字段：department_id ,department_name ,location 其中department_id是主键我想查询每个每个部门的编号，部门名称，部门人员的平均收入，然后排序。请各位大侠帮帮忙。

Answer 1

--try it
select e.department_id,d.department_name ,sum(e.salay)/count(1) as ave_salay from employees  e,department d where e.department_id=d.department_id  group by  e.department_id,d.department_name

Answer 2

select b.department_id 部门编号,b.department_name 部门名称,a.employees_name 员工姓名,avg(a.salay) 部门人员平均收入
  from employees a,department b 
 where a.department_id=b.department_id
 group by b.department_id,b.department_name,a.employees_name
 order by a.salay; 

Answer 3

弄错了。
select b.department_id 部门编号,b.department_name 部门名称,a.employees_name 员工姓名,sum(a.salay)/count(1) 部门人员平均收入 
  from employees a,department b 
where a.department_id=b.department_id 
group by b.department_id,b.department_name,a.employees_name 
order by a.salay; 

Answer 4

select b.department_id,b.department_name,avg(a.salary) avg_salary
from employees a,department b
where a.department_id = b.department_id
group by b.department_id,b.department_name

Answer 5

SELECT B.department,AVG(A.salay) AVG_SAL FROM employees  A LEFT JOIN department B ON A.department_id=B.department_id

Answer 6

select 
department.department_id,
department.department_name，
avg(employees.salay) 
from 
employees,department
where 
department.department_id= employees.department_id
group by 
department.department_id
order by
department.department_id