10 laksh records and need to find out the top5 salary

Question

Hi,
I have emp table with 10 laksh records and need to find out the top5 salary.I formed the below mentioned query,
SELECT ROWNUM,SAL,EMPNO,ENAME,DEPTNO FROM(SELECT ENAME,EMPNO,
DEPTNO,SAL FROM EMP ORDER BY SAL DESC) WHERE ROWNUM<=3 AND SAL IS NOT NULL;
i would like tune this query or anyother new qeury find out top5 salary.
By
Siva

Answer 1

kn_sivaraman wrote:
Hi,
I have emp table with 10 laksh records and need to find out the top5 salary.I formed the below mentioned query,
SELECT ROWNUM,SAL,EMPNO,ENAME,DEPTNO FROM(SELECT ENAME,EMPNO,
DEPTNO,SAL FROM EMP ORDER BY SAL DESC) WHERE ROWNUM<=3 AND SAL IS NOT NULL;
i would like tune this query or anyother new qeury find out top5 salary.
By
SivaWhy do you need to Tune? What do you need to tune?
What is the execution time of the query? What is the explain plan?
Moreover, in an International forum, refrain from using Locals. 10 Lakhs = 1 Million.
Do provide the above details to determine if your query needs tuning?
Below is a correct version of Top N query. Untested for your example. Please do modify according to your needs.
SELECT ROWNUM,
  SAL,
  EMPNO,
  ENAME,
  DEPTNO
FROM
  (SELECT ENAME,EMPNO, DEPTNO,SAL, dense_rank() over(order by sal desc nulls last) dr
    FROM EMP ORDER BY SAL DESC
  ) a
WHERE a.dr <= 5;Regards,
P.