PARTITION BY

SELECT deptno 部门名称 ,ename 员工姓名, sal 员工工资, SUM(sal) OVER(PARTITION BY deptno ORDER BY sal) 所在部门工资总和  FROM emp;  

场景：查询出每个部门工资最低的员工编号【每个部门可能有两个最低的工资员工】  

create table TSALER
(
  userid NUMBER(10),
  salary NUMBER(10),
  deptid NUMBER(10)
)

-- Add comments to the columns 
comment on column TSALER.userid
  is '员工ID';
comment on column TSALER.salary
  is '工资';
comment on column TSALER.deptid
  is '部门ID';

insert into TSALER (工号, 工资, 部门编号)
values (1, 200, 1);

insert into TSALER (工号, 工资, 部门编号)
values (2, 2000, 1);

insert into TSALER (工号, 工资, 部门编号)
values (3, 200, 1);

insert into TSALER (工号, 工资, 部门编号)
values (4, 1000, 2);

insert into TSALER (工号, 工资, 部门编号)
values (5, 1000, 2);

insert into TSALER (工号, 工资, 部门编号)
values (6, 3000, 2);

方法一：

select tsaler.* from tsaler 
inner join(select min(salary) as salary,deptid from tsaler group by deptid) c
on tsaler.salary=c.salary and tsaler.deptid=c.deptid 

方法二：

select * from tsaler 
inner join(select min(salary) as salary,deptid from tsaler group by deptid) c
using(salary,deptid)

方法三：

--row_number() 顺序排序
select row_number() over(partition by deptid order by salary) my_rank ,deptid,USERID,salary from tsaler;
--rank() （跳跃排序，如果有两个第一级别时，接下来是第三级别）
select rank() over(partition by deptid order by salary) my_rank,deptid,USERID,salary from tsaler;
--dense_rank（）（连续排序，如果有两个第一级别时，接下来是第二级）
select dense_rank() over(partition by deptid order by salary) my_rank,deptid,USERID,salary from tsaler;
-------方案3解决方案
select * from (select rank() over(partition by deptid order by salary) my_rank,deptid,USERID,salary from tsaler) where my_rank=1;
select * from (select dense_rank() over(partition by deptid order by salary) my_rank,deptid,USERID,salary from tsaler) where my_rank=1;