Common Table Expressions (CTEs)
CTEs provide a readable and reusable way to define temporary result sets, facilitating the selection of top N rows per group.
Query:
WITH ranked_data AS (
SELECT *,
ROW_NUMBER() OVER (PARTITION BY area ORDER BY sales_num DESC) AS row_value.
FROM sales_data
)
SELECT *
FROM ranked_data
WHERE row_num <= 2;
Output:
Explanation: The output selects the top 2 rows per area from the sales_data table, ordered by sales number in descending order, utilizing a common table expression to assign row numbers.
How to Restrict Results to top N Rows per Group in PL/SQL?
In the world of database administration, retrieving top N rows from every grouping is a frequent but complicated one. Whether you are performing cross-tabulations with large datasets or looking for specific insights within the grouping of data, the ability to restrict the output to top N rows per group is precious.
Implementing this job in PL/SQL, which is Oracle’s procedural extension to SQL, may call for a thought-out approach applying approaches customized for the database environment. Now is the time to explore a how-to and a methodology for determining top N results per group in PL/SQL.