What is recursive programming?
Recursive programming is a technique where a function calls itself.
How to use recursion in SQL
SQL supports recursion through the use of common table expressions (CTEs). CTEs are temporary named result sets that can be referenced in the FROM clause of a query. Recursive CTEs allow you to define a query that references itself, which allows you to perform recursive tasks and queries.
Examples
1. The following example shows a recursive query to calculate the sum of all the numbers from 1 to 10:
WITH recursive sum_of_numbers(n, result) AS (
SELECT 1, 1
UNION ALL
SELECT n + 1, result + (n + 1)
FROM sum_of_numbers
WHERE n < 10
)
SELECT result
FROM sum_of_numbers
ORDER BY n DESC
LIMIT 1;2. The following example shows a recursive query to get the list of days in the current month:
WITH RECURSIVE `days` AS
(
SELECT 1 AS `day` UNION ALL SELECT `day` + 1 FROM `days` WHERE `day` < DAY(LAST_DAY(NOW()))
)
SELECT * FROM `days`Benefits of using recursion in SQL
Recursion can provide a number of benefits in SQL, including:
- It can simplify complex queries by breaking them down into smaller, more manageable subqueries.
- It can improve the performance of some queries by avoiding the need to use temporary tables or cursors.
- It can make your code more concise and elegant.
Conclusion
Recursion is a powerful technique that can be used to solve a wide range of problems in SQL. It can simplify complex queries, improve performance, and make your code more concise and elegant. If you are working with hierarchical or graph-based data, recursion is a technique that you should definitely learn.