问题
In Oracle 11g we need to be able to query a table to pull out information from rows with the highest and lowest values in a certain group. For example using the EMP table we'd like to find the name of person with the highest salary and the name of the person with the lowest salary in each department
DEPTNO MAX_SAL MAX_EARNER MIN_SAL MIN_EARNER
-------------------------------------------------------
10 5000 KING 1300 MILLER
20 3000 FORD 2975 JONES
etc
(if there are two or more staff with the highest or lowest salaray we want to always return the first in alphabetical order).
A Previous Post discussed how to get a value for just the maximum but not both max and min.
We have an untidy solution at the moment based on the link above then applying subsiquent queries but performance is important to us. I predict a good solution will also require analytic functions and possibly a pivot to coalesce the multiple rows into single rows.
Any help greatly appreciated! Richard
回答1:
This is easily solvable with analytic functions. As you can see, there are two employees earning the maximum salary in DEPT 20; this is an important detail, as some common solutions to this kind of problem miss that information.
SQL> select ename
2 , deptno
3 , sal
4 from (
5 select ename
6 , deptno
7 , sal
8 , max (sal) over (partition by deptno) max_sal
9 , min (sal) over (partition by deptno) min_sal
10 from emp
11 )
12 where sal = max_sal
13 or sal = min_sal
14 order by deptno, sal
15 /
ENAME DEPTNO SAL
---------- ---------- ----------
KISHORE 10 1300
SCHNEIDER 10 5000
CLARKE 20 800
RIGBY 20 3000
GASPAROTTO 20 3000
HALL 30 950
LIRA 30 3750
TRICHLER 50 3500
FEUERSTEIN 50 4500
9 rows selected.
SQL>
Oops, I missed an important detail about the result format. My data won't fit the requested output, because there are two employees earning the maximum salary. So this query, which I admit is a bit awkward, gives us the required layout. The MIN() on the employee names returns the alphabetical order :
SQL> select
2 deptno
3 , max (case when sal = min_sal then min_sal else null end ) as min_sal
4 , min (case when sal = min_sal then ename else null end ) as min_name
5 , max (case when sal = max_sal then max_sal else null end ) as max_sal
6 , min (case when sal = max_sal then ename else null end ) as max_name
7 from (
8 select ename
9 , deptno
10 , sal
11 , max (sal) over (partition by deptno) max_sal
12 , min (sal) over (partition by deptno) min_sal
13 from emp
14 )
15 where sal = max_sal
16 or sal = min_sal
17 group by deptno
18 order by deptno
19 /
DEPTNO MIN_SAL MIN_NAME MAX_SAL MAX_NAME
---------- ---------- ---------- ---------- ----------
10 1300 KISHORE 5000 SCHNEIDER
20 800 CLARKE 3000 GASPAROTTO
30 950 HALL 3750 LIRA
50 3500 TRICHLER 4500 FEUERSTEIN
SQL>
I don't like this solution. Most datasets will contain such clashes, and we need to acknowledge them. Filtering the result on the basis of some unrelated criteria to fit a Procrustean report layout is misleading. I would prefer a report layout which reflected the whole dataset. Ultimately it depends on the business purpose which the query serves. And, of course, the customer is always right 8-)
回答2:
You can use the below query
SELECT
dept,
max_sal,
(SELECT emp_name FROM emp WHERE salary = max_sal AND rownum =1) max_earner,
min_sal,
(SELECT emp_name FROM emp WHERE salary = min_sal AND rownum =1) min_earner
FROM
(SELECT
dept,
MAX(salary) max_sal,
MIN(salary) min_sal
FROM emp
GROUP BY dept);
assuming your table looks like this:
CREATE TABLE emp
(
dept NUMBER,
emp_name VARCHAR2(20 BYTE),
salary NUMBER
);
Update
In order to acheive your other requirement "if there are two or more staff with the highest or lowest salaray we want to always return the first in alphabetical order", you may tweak the query a bit as below (I'm sure there's scope for improvement here):
SELECT
dept,
max_sal,
(select emp_name from (SELECT * FROM emp order by emp_name asc) WHERE salary = max_sal AND rownum =1) max_earner,
min_sal,
(select emp_name from (SELECT * FROM emp order by emp_name asc) WHERE salary = min_sal AND rownum =1) min_earner
FROM
(SELECT
dept,
MAX(salary) max_sal,
MIN(salary) min_sal
FROM emp
GROUP BY dept);
来源：https://stackoverflow.com/questions/5880708/getting-values-relating-to-the-max-and-min-rows-in-oracle