--求和兩種結果相同
select e.employee_id ,e.first_name,e.salary,sum(e.salary)
from employees e
group by e.employee_id ,e.first_name,e.salary;
select e.employee_id ,e.first_name,e.salary,sum(e.salary) over() sum
from employees e;
--求和
--第二行的sum=第一行裡的sal+第二行裡的sal;
-- 第二行的sum=第一行裡的sal+第二行裡的sal+第三行裡的sal;
select e.employee_id,
e.department_id,
e.first_name,
e.salary,
sum(e.salary) over(order by e.first_name) sum
from employees e;
--結果如圖
--每個sum的值都是把last_name相同的sal值進行求和。
SELECT e.employee_id,
e.department_id,
e.last_name,
e.salary,
SUM(e.salary) over(PARTITION BY e.last_name) SUM
FROM employees e;
--結果如圖