【Oracle】oracle取最大值和最小值的几个方法汇总

时间：2015-01-06 11:41:12 收藏：0 阅读：9971

（1）oracle使用keep分析函数取最值记录

-- 取工资sal最大的雇员姓名及其工资，以及工资sal最少的雇员姓名及其工资
select 
       deptno,
       empno,
       ename,
       sal,
       max(ename) keep(dense_rank FIRST order by sal) over (partition by deptno) as min_sal_man,
       max(sal) keep(dense_rank FIRST order by sal) over (partition by deptno) as min_sal,
       max(ename) keep(dense_rank LAST order by sal) over (partition by deptno) as max_sal_man,
       max(sal) keep(dense_rank LAST order by sal) over (partition by deptno) as max_sal
from emp
where deptno=10

结果如下：

技术分享

从语句中可以看到，ename和sal都是用的max()，这样做的目的是为了去除由于keep()函数得到的有重复值的数据结果集。这样用有一个弊端，加入部门20有两个相同的最大SAL的人，部门30有两个相同的最小SAL的人，如果按照这种方法取出来的数据，就不一定准确了，重复的人会被去除掉。

我们用下面的语句来修改一下：

select 
       deptno,
       empno,
       ename,
       sal,
       max(ename) keep(dense_rank FIRST order by sal) over (partition by deptno) as min_sal_man,
       max(sal) keep(dense_rank FIRST order by sal) over (partition by deptno) as min_sal,
       max(ename) keep(dense_rank LAST order by sal) over (partition by deptno) as max_sal_man,
       max(sal) keep(dense_rank LAST order by sal) over (partition by deptno) as max_sal,
       wmsys.wm_concat(ename) keep(dense_rank LAST order by sal) over (partition by deptno) as 工资最高的人,
       wmsys.wm_concat(ename) keep(dense_rank FIRST order by sal) over (partition by deptno) as 工资最低的人
from emp
where deptno=20
order by 1, 2 ;

我们新增了两个列：工资最高的人，工资最低的人。执行看一下结果：

技术分享

可以看到，deptno=20时，SCOTT和FORD两个人的工资SAL都是3000，如果用MAX()就只能取出其中一个人的姓名，显然是不对的。

然后，我们再来看一下deptno=30时的情况：

select 
       deptno,
       empno,
       ename,
       sal,
       max(ename) keep(dense_rank FIRST order by sal) over (partition by deptno) as min_sal_man,
       max(sal) keep(dense_rank FIRST order by sal) over (partition by deptno) as min_sal,
       max(ename) keep(dense_rank LAST order by sal) over (partition by deptno) as max_sal_man,
       max(sal) keep(dense_rank LAST order by sal) over (partition by deptno) as max_sal,
       wmsys.wm_concat(ename) keep(dense_rank LAST order by sal) over (partition by deptno) as 工资最高的人,
       wmsys.wm_concat(ename) keep(dense_rank FIRST order by sal) over (partition by deptno) as 工资最低的人
from emp
where deptno=30
order by 1, 2 ;

deptno=30时的结果如下：

技术分享

可以看到，deptno=30时，WARD和MARTIN两人的工资最小且均为1250，如果用MAX()的方式，就只能取出其中一个人的名称。

这就是因为keep()取出来的数据集是包含多个数据结果的，所以，在语句中使用了wmsys.wm_concat()函数，该函数的作用是以逗号分隔连接列的值。

注：wm_concat()的功能有点儿类似分析函数listagg() within group() 。

（2）使用SQL子查询和聚合函数，查询出最大值和最小值

-- 使用子查询查询出最大值和最小值
select * from 
 (
  select 
         deptno,
         listagg(ename,‘,‘) within group (order by deptno) as dept_max_ename,
         max(sal) as dept_max_sal
  from emp 
  where (deptno,sal) in (select deptno, max(sal) as max_sal from emp group by deptno)
  group by deptno
 ) A
inner join 
 (
  select 
         deptno,
         listagg(ename,‘,‘) within group (order by deptno) as dept_min_ename,
         min(sal) as dept_min_sal
  from emp 
  where (deptno,sal) in (select deptno, min(sal) as min_sal from emp group by deptno)
  group by deptno
 ) B
on A.deptno = B.deptno

结果如下：

技术分享

在这个方案里面，还使用了listagg()分析函数将最值有重复姓名的人合并在一起，用wm_concat()函数替代listagg()也可以

wm_concat(ename) as dept_max_ename,
wm_concat(ename) as dept_min_ename,

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