How to Retrieve the Top 5 Column Values in Oracle SQL?

Oracle SQL: Extracting the Top 5 Highest Values

Many database tasks require retrieving a specific number of rows based on a column's highest or lowest values. This is especially helpful for identifying top performers or creating reports. This article demonstrates several Oracle SQL methods for retrieving the top 5 values from a column.

Using Analytic Functions: RANK() and DENSE_RANK()

Analytic functions offer efficient row ranking. RANK() assigns a unique rank based on specified criteria, while DENSE_RANK() provides similar functionality but eliminates gaps in ranking for ties.

To retrieve the top 5 salaries from the "emp" table's "sal" column using RANK():

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

Leveraging ROW_NUMBER()

The ROW_NUMBER() function assigns a sequential number to each row, regardless of ordering. This can limit results to a specific row count.

Here's how to get the top 5 salaries using ROW_NUMBER():

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

Alternative Approach: The ROWNUM Pseudocolumn

The ROWNUM pseudocolumn provides the physical row number in query results. However, its use for limiting results is generally discouraged due to potential inconsistencies.

An example using ROWNUM:

SELECT *
FROM (
    SELECT empno, sal
    FROM emp
    ORDER BY sal DESC
)
WHERE ROWNUM <= 5;

Choosing the Right Method

The best approach depends on specific needs and data characteristics.

• RANK() and DENSE_RANK() preserve ranking order, even with ties.
• ROW_NUMBER() guarantees a specific number of rows but may arbitrarily truncate tied results.
• ROWNUM is less reliable and should be used cautiously.

Careful consideration of these methods is crucial for accurate and consistent data retrieval in Oracle SQL.

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