I want to query difference between first and second highest salary - sql

Question

I already got the second-highest salary.
I would like to display: employee name, salary, department name, and the difference between the highest and second-highest salary.
Here is my current code.
select max(SAL) SecondHighestSalary
from EMP A, DEPT B
where SAL < (
select max(A.SAL)
from EMP A, DEPT B
where A.DEPTNO = B.DEPTNO and B.LOC = 'New York'
);
Thanks

Answer 1

Use the DENSE_RANK (if you want highest two unique salary values) or ROW_NUMBER (if you want the salary of the two highest earning people regardless of ties) analytic functions and then use conditional aggregation:
SELECT MAX( CASE WHEN sal_rank = 1 THEN sal END )
- MAX( CASE WHEN sal_rank = 2 THEN sal END ) AS sal_difference_ignore_ties,
MAX( CASE WHEN sal_rownum = 1 THEN sal END )
- MAX( CASE WHEN sal_rownum = 2 THEN sal END ) AS sal_difference_with_ties
FROM (
SELECT e.deptno,
e.sal,
DENSE_RANK() OVER ( ORDER BY e.sal DESC ) AS sal_rank,
ROW_NUMBER() OVER ( ORDER BY e.sal DESC ) AS sal_rownum
FROM emp e
INNER JOIN dept d
ON ( e.deptno = d.deptno )
WHERE d.loc = 'New York'
);
Which, for the sample data:
CREATE TABLE emp ( deptno, sal ) AS
SELECT 1, 2000 FROM DUAL UNION ALL
SELECT 1, 2000 FROM DUAL UNION ALL
SELECT 1, 1000 FROM DUAL UNION ALL
SELECT 1, 500 FROM DUAL UNION ALL
SELECT 1, 200 FROM DUAL UNION ALL
SELECT 2, 2000 FROM DUAL UNION ALL
SELECT 2, 1500 FROM DUAL UNION ALL
SELECT 2, 200 FROM DUAL UNION ALL
SELECT 2, 700 FROM DUAL;
CREATE TABLE dept ( deptno, loc ) AS
SELECT 1, 'New York' FROM DUAL UNION ALL
SELECT 2, 'Beijing' FROM DUAL;
Outputs:
SAL_DIFFERENCE_IGNORE_TIES | SAL_DIFFERENCE_WITH_TIES
-------------------------: | -----------------------:
1000 | 0
Or, if you want all the departments:
SELECT deptno,
MAX( CASE WHEN sal_rank = 1 THEN sal END )
- MAX( CASE WHEN sal_rank = 2 THEN sal END ) AS sal_difference_ignore_ties,
MAX( CASE WHEN sal_rownum = 1 THEN sal END )
- MAX( CASE WHEN sal_rownum = 2 THEN sal END ) AS sal_difference_with_ties
FROM (
SELECT e.deptno,
e.sal,
DENSE_RANK() OVER ( PARTITION BY e.deptno ORDER BY e.sal DESC ) AS sal_rank,
ROW_NUMBER() OVER ( PARTITION BY e.deptno ORDER BY e.sal DESC ) AS sal_rownum
FROM emp e
INNER JOIN dept d
ON ( e.deptno = d.deptno )
)
GROUP BY deptno;SELECT deptno,
MAX( CASE WHEN sal_rank = 1 THEN sal END )
- MAX( CASE WHEN sal_rank = 2 THEN sal END ) AS sal_difference_ignore_ties,
MAX( CASE WHEN sal_rownum = 1 THEN sal END )
- MAX( CASE WHEN sal_rownum = 2 THEN sal END ) AS sal_difference_with_ties
FROM (
SELECT e.deptno,
e.sal,
DENSE_RANK() OVER ( PARTITION BY e.deptno ORDER BY e.sal DESC ) AS sal_rank,
ROW_NUMBER() OVER ( PARTITION BY e.deptno ORDER BY e.sal DESC ) AS sal_rownum
FROM emp e
INNER JOIN dept d
ON ( e.deptno = d.deptno )
)
GROUP BY deptno;
Which outputs:
DEPTNO | SAL_DIFFERENCE_IGNORE_TIES | SAL_DIFFERENCE_WITH_TIES
-----: | -------------------------: | -----------------------:
1 | 1000 | 0
2 | 500 | 500
db<>fiddle here

Answer 2

How about this?
Based on Scott's EMP table:
SQL> select ename, sal
2 from emp
3 order by sal desc;
ENAME SAL
---------- ----------
KING 5001 --> highest salary
FORD 3000 --> Ford and Scott share the
SCOTT 3000 --> 2nd highest salary
JONES 2975
BLAKE 2850
CLARK 2450
ALLEN 1600
TURNER 1500
MILLER 1300
WARD 1250
MARTIN 1250
ADAMS 1100
SMITH 1000
JAMES 950
14 rows selected.
Then you'd rank them and - using LISTAGG (to display all employees that share the same highest or second highest salary) - get the final result:
SQL> with temp as
2 (select e.ename,
3 e.sal,
4 dense_rank() over (order by e.sal desc) rnk,
5 d.dname
6 from emp e join dept d on d.deptno = e.deptno
7 )
8 select listagg(case when rnk = 1 then ename ||' - '|| dname || ' ($' || sal ||')' end, ', ')
9 within group (order by ename) highest,
10 --
11 listagg(case when rnk = 2 then ename ||' - '|| dname || ' ($' || sal ||')' end, ', ')
12 within group (order by ename) second_highest,
13 --
14 max(case when rnk = 1 then sal end) -
15 max(case when rnk = 2 then sal end) diff
16 from temp t
17 where t.rnk in (1, 2);
HIGHEST SECOND_HIGHEST DIFF
------------------------------ -------------------------------------------------- ----------
KING - ACCOUNTING ($5001) FORD - RESEARCH ($3000), SCOTT - RESEARCH ($3000) 2001
SQL>