How to do the Recursive SELECT query in MySQL?

sql

recursive-procedures

best-practices

stored-procedures

byAlex Kataev·Sep 29, 2024

For a recursive SELECT in MySQL, utilize the WITH RECURSIVE structure to define a Common Table Expression (CTE) that self-queries. Here's a simplified example showcasing recursive data retrieval:

WITH RECURSIVE lineage AS (
    SELECT id, parent_id
    FROM family -- Replace with your table
    WHERE id = 1 -- Starting point...it's me! 
    UNION ALL
    SELECT f.id, f.parent_id
    FROM family f
    JOIN lineage l ON l.id = f.parent_id -- Hey, mom and dad!
)
SELECT * FROM lineage; -- Hi family!

In this script, swap family with your target table, id with your unique column, and parent_id with the column representing the next hierarchical level. The statement initiates from a target row (WHERE id = 1) and recursively incorporates successive rows up until no further ones exist.

Debut with recursion in MySQL

Recursion in MySQL is synonymous with a chain of thoughts, where each thought triggers countless others. It's a mechanism of self-referencing, where a function either directly or indirectly invokes itself.

Central considerations for recursion

While constructing recursive queries, consider:

Session-bound temp tables: This ensures data isn't mixed up amongst users.
Separators: Effectively distinguish the primary logic from the recursive UNION.
Prevent infinite recursion: Use conditions to put a brake on potential ceaseless looping.

Effective trends for recursion in MySQL

In your journey of recursive queries, remember:

Origination points: Customize the start point based on user-driven recursion.
Dynamic SQL: Boost adaptability by structuring queries that respond based on input.
Loop management: Use a variable to ward off infinite ancestral recursion.

Hindrances to lookout for

Be cautious about:

Data irregularities: Such as null values or data loops that might conclude the recursion before expected.
Efficiency degradation: Profound or elaborate tree structures might intensify the retrieval duration.

Recursive procedures and best practices

To employ a recursive search with stored procedures in MySQL, you can use a cocktail of dynamic SQL, temporary tables, and while loops. Here's a condensed instance of a stored procedure that leverages recursion in MySQL:

DELIMITER //
CREATE PROCEDURE RecursiveSearch(IN pParentId INT) -- Paging Dr. Search!
BEGIN
    DROP TEMPORARY TABLE IF EXISTS TempResults; -- Clear the operating table!

    CREATE TEMPORARY TABLE TempResults(
        id INT,
        parent_id INT
    );

    SET @pv := pParentId; -- Paging Dr. Search! You have a call on line 1! 

    WHILE @pv IS NOT NULL DO
        INSERT INTO TempResults(id, parent_id)
        SELECT id, parent_id
        FROM categories
        WHERE parent_id = @pv; -- No parent left behind!

        SET @pv := (SELECT id FROM TempResults WHERE id = @pv LIMIT 1); -- Dial M for More!
    END WHILE;

    SELECT * FROM TempResults; -- Paging Dr. User! Your results are in!
END //
DELIMITER ;

Invoke this stored procedure with the desired parent ID:

CALL RecursiveSearch(1); -- Paging Dr. Search! You're needed in Room 1!

This recursive stored procedure wraps up the search logic, assuring precise data by using a session-tied temporary table and facilitating variable search based on user input.