How to Retrieve the Top 5 Highest Values from an Oracle SQL Column?

Extracting the Top 5 Highest Values from an Oracle SQL Column

This guide demonstrates how to efficiently retrieve the top five highest values from a specific column within your Oracle SQL database. We'll explore several approaches using analytic functions and a non-analytic method.

Methods Utilizing Analytic Functions:

The RANK(), DENSE_RANK(), and ROW_NUMBER() functions provide powerful ways to rank rows based on a column's values.

1. Using RANK():

SELECT * FROM (
    SELECT empno, sal, RANK() OVER (ORDER BY sal DESC) AS rnk
    FROM emp
)
WHERE rnk <= 5;

The RANK() function assigns ranks based on the descending order of salaries (sal). Rows with equal salaries receive the same rank, resulting in gaps in the ranking sequence.

2. Using DENSE_RANK():

SELECT * FROM (
    SELECT empno, sal, DENSE_RANK() OVER (ORDER BY sal DESC) AS rnk
    FROM emp
)
WHERE rnk <= 5;

DENSE_RANK() is similar to RANK(), but it assigns consecutive ranks without gaps, even when ties exist.

3. Using ROW_NUMBER():

SELECT * FROM (
    SELECT empno, sal, ROW_NUMBER() OVER (ORDER BY sal DESC) AS rnk
    FROM emp
)
WHERE rnk <= 5;

ROW_NUMBER() assigns a unique rank to each row based on the specified order. Use caution with ties, as it might arbitrarily exclude some rows.

Non-Analytic Approach (Using ROWNUM):

A simpler, yet less robust, method involves using ROWNUM:

SELECT * FROM emp
WHERE ROWNUM <= 5
ORDER BY sal DESC;

This approach orders the data by salary and then limits the result set to the first five rows. However, ROWNUM is applied before the ORDER BY clause, potentially leading to incorrect results if there are ties in the salary values. This method is generally less reliable than the analytic function approaches. Therefore, using RANK(), DENSE_RANK(), or ROW_NUMBER() is strongly recommended for accurate and consistent results.

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