Recursive stored functions in MySQL

MySQL does not allow recursive FUNCTIONs, even if you set max_sp_recursion_depth.

It does allow up to 255 recursion in a PROCEDURE if you set max_sp_recursion_depth.

So I recommend that you replace your function with a procedure, using an INOUT variable for the return_path.

From the stored procedure in your question, *with the help from @Ike Walker,

DROP PROCEDURE IF EXISTS getPath;DELIMITER $$CREATE PROCEDURE getPath(IN category_id INT UNSIGNED, OUT return_path TEXT)BEGIN    DECLARE parent_id INT UNSIGNED;    DECLARE path_result TEXT;    SET max_sp_recursion_depth=50;    SELECT CONCAT('/', ac.name), ac.parent_id INTO return_path, parent_id FROM article_categories AS ac WHERE ac.id = category_id;    IF parent_id > 0 THEN        CALL getPath(parent_id, path_result);        SELECT CONCAT(path_result, return_path) INTO return_path;    END IF;END $$DELIMITER ;

Create a function:

DROP FUNCTION IF EXISTS getPath;CREATE FUNCTION getPath(category_id INT) RETURNS TEXT DETERMINISTICBEGIN    DECLARE res TEXT;    CALL getPath(category_id, res);    RETURN res;END$$

Next, you can select:

SELECT category_id, name, getPath(category_id) AS path FROM article_categories ;