Oracle SQL - How to Retrieve highest 5 values of a column

Question

How do you write a query where only a select number of rows are returned with either the highest or lowest column value.

i.e. A report with the 5 highest salaried employees?

Answer 1

The best way to do this is with analytic functions, RANK() or DENSE_RANK() ...

SQL> select * from (
  2        select empno
  3               , sal
  4               , rank() over (order by sal desc) as rnk
  5        from emp)
  6  where rnk <= 5
  7  /

     EMPNO        SAL        RNK
---------- ---------- ----------
      7839       5000          1
      7788       3000          2
      7902       3000          2
      7566       2975          4
      8083       2850          5
      7698       2850          5

6 rows selected.

SQL>

DENSE_RANK() compresses the gaps when there is a tie:

SQL> select * from (
  2        select empno
  3               , sal
  4               , dense_rank() over (order by sal desc) as rnk
  5        from emp)
  6  where rnk <= 5
  7  /

     EMPNO        SAL        RNK
---------- ---------- ----------
      7839       5000          1
      7788       3000          2
      7902       3000          2
      7566       2975          3
      8083       2850          4
      7698       2850          4
      8070       2500          5

7 rows selected.

SQL>

Which behaviour you prefer depends upon your business requirements.

There is also the ROW_NUMBER() analytic function which we can use to return a precise number of rows. However, we should avoid using solutions based on row number unless the business logic is happy to arbitrarily truncate the result set in the event of a tie. There is a difference between asking for the five highest values and the first five records sorted by high values

There is also a non-analytic solution using the ROWNUM pseudo-column. This is clunky because ROWNUM is applied before the ORDER BY clause, which can lead to unexpected results. There is rarely any reason to use ROWNUM instead of ROW_NUMBER() or one of the ranking functions.