求各部门的工资最大值的各种实现方法

 

----列出部门ID和最大薪资值
---1 最常规的方法
select e.deptno, max(e.sal)
  from emp e
 group by e.deptno;
---2、分析函数实现
select *
  from (select e.deptno,
               e.sal,
               row_number() over(partition by e.deptno order by e.sal desc) as rn
          from emp e)
 where rn = 1;
 ---备注：row_number()over() 分析函数如果存在重复的salary的话 会被过滤掉

---需求更改成：列出各部门最高薪资以部门id
/*这个是后才有方法1的实现方式肯定不行
*/
---方法1的实现(不可以)
select e.deptno,e.ename  ,max(e.sal)
  from emp e
 group by e.department_id,e.ename;---group by 里面不能使用别名，order by 可以
 
---子查询方法实现
select e.sal, e.deptno
  from emp e
 where (e.deptno, e.sal) in
       (select em.deptno, max(em.sal)
          from emp em
         group by em.deptno)
        
---分析函数实现（不过滤重复值）
select *
  from (select e.department_id,
               e.salary,
               dense_rank() over(partition by e.department_id order by e.salary desc) as rn
          from employees e)
 where rn = 1;---employees 表最大工资不存在重复的 ，我们换一个emp
 
 ----也取最大重复值
select *
  from (select e.deptno,
               e.sal,
               dense_rank() over(partition by e.deptno order by e.sal desc) as rn
          from emp e)
 where rn = 1;
 
 ----不取最大重复值
 select *
  from (select e.deptno,
               e.sal,
               row_number() over(partition by e.deptno order by e.sal desc) as rn
          from emp e)
 where rn = 1;
 
----max()over() 函数实现
 select *
  from (select e.deptno,
               e.sal,
               max(e.sal) over(partition by e.deptno order by e.sal desc) as rn
          from emp e)
 where rn = sal;

 

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