over partition by 與 group by 都是與統計類函數用，這兩個有什么區別呢？
目前我只知道一個這樣的區別：
比如有一張表saraly:CREATE TABLE SALARY AS SELECT 'A' NAME,10 DEPT,1000 SALARY FROM DUAL UNION ALL SELECT 'B',10,2000 FROM DUAL UNION ALL SELECT 'C' ,20,1500 FROM DUAL UNION ALL SELECT 'D',20,3000 FROM DUAL UNION ALL
SELECT 'E',10,1000 FROM DUAL;
NAME DEPT SALARY
A 10 1000
B 10 2000
C 20 1500
D 20 3000
E 10 1000
用over partition by 我就可以查詢到每位員工本來的具體信息和它所在部門的總工資：
select name,dept,salary,sum(salary) over (partition by dept) total_salary from salary;
name dept salary tatal_salary
A 10 1000 4000
B 10 2000 4000
E 10 1000 4000
C 20 1500 4500
D 20 3000 4500
用goup by 就沒辦法做到這點，只能查詢到每個部門的總工資：
select dept,sum(salary) total_salary from salary group by dept
dept total_salary
10 4000
20 4500
另外over partion by 還可以做到查詢每位員工占部門總工資的百分比：
select name,dept,salary,salary*100/sum(salary) over (partition by dept) percent from salary;
name dept salary percent
A 10 1000 25
B 10 2000 50
E 10 1000 25
C 20 1500 33.3333333333333
D 20 3000 66.6666666666667