編寫SQL查詢返回表

Question

我想寫一個SQL查詢返回一個表，該表包含表中僱傭至少一名員工的所有部門，他們僱用的人數以及每個部門的薪水總和，按部門ID責令

部門：

dept_id | dept_name | dept_location 
10  | Accounts | Delhi 
20  | Marketing | Delhi 
40  | IT  | Warsaw 
30  | production| Hyderabad 
5O  | Sales  | Bengaluru 

員工：

emp_id | emp_name | dept_id | salary 
1  | Jojo  | 20  | 5000 
2  | Popat Lal | 30  | 15000 
3  | Santa Singh| 40  | 25000 
4  | Banta Singh| 20  | 7500 
5  | Soban Lal | 20  | 15000 
6  | Kk  | 10  | 12000 
7  | Bob  | 20  | 35000 
8  | John  | 30  | 25000 
9  | Smith  | 40  | 5000 

查詢應返回：

dept_id | count  | sum_of_salary 
10  | 1   | 12000 
20  | 4   | 62500 
30  | 2   | 40000 
40  | 2   | 30000 

Answer 1

這僅僅是簡單的group by：

select dept_id, 
    count(*) cnt, 
    sum(salary) sum_of_salary 
from employee 
group by dept_id 
order by dept_id; 

Answer 2

select d.dept_id, d.dept_name, count(*) total_hires, sum(salary) total_salary 
from employee e join department d on e.dept_id = d.dept_id 
group by d.dept_id, d.dept_name