mysql stored procedure that calls itself recursively

Question

I have the following table:

id | parent_id | quantity
-------------------------
1  | null      | 5
2  | null      | 3
3  | 2         | 10
4  | 2         | 15
5  | 3         | 2
6  | 5         | 4
7  | 1         | 9

Now I need a stored procedure in mysql that calls itself recursively and returns the computed quantity. For example the id 6 has 5 as a parent which as 3 as a parent which has 2 as a parent. So I need to compute 4 * 2 * 10 * 3 ( = 240) as a result.

I am fairly new to stored procedures and I won't use them very often in the future because I prefer having my business logic in my program code rather then in the database. But in this case I can't avoid it.

Maybe a mysql guru (that's you) can hack together a working statement in a couple of seconds.

Answer 1

its work only in mysql version >= 5

the stored procedure declaration is this,

you can give it little improve , but this working :

DELIMITER $$

CREATE PROCEDURE calctotal(
   IN number INT,
   OUT total INT
)

BEGIN

   DECLARE parent_ID INT DEFAULT NULL ;
   DECLARE tmptotal INT DEFAULT 0;
   DECLARE tmptotal2 INT DEFAULT 0;

   SELECT parentid   FROM test   WHERE id = number INTO parent_ID;   
   SELECT quantity   FROM test   WHERE id = number INTO tmptotal;     

   IF parent_ID IS NULL
    THEN
    SET total = tmptotal;
   ELSE     
    CALL calctotal(parent_ID, tmptotal2);
    SET total = tmptotal2 * tmptotal;   
   END IF;

END$$

DELIMITER ;

the calling is like (its important to set this variable) :

SET @@GLOBAL.max_sp_recursion_depth = 255;
SET @@session.max_sp_recursion_depth = 255; 

CALL calctotal(6, @total);
SELECT @total;

Answer 2

Take a look at Managing Hierarchical Data in MySQL by Mike Hillyer.

It contains fully worked examples on dealing with hierarchical data.