Recursive mysql select?

Question

I saw this answer and i hope he is incorrect, just like someone was incorrect telling primary keys are on a column and I can\'t set it on multiple columns.

Here is m

Answer 1

I know there is probably better and more efficient answer above but this snippet gives a slightly different approach and provides both - ancestors and children.

The idea is to constantly insert relative rowIds into temporary table, then fetch a row to look for it's relatives, rinse repeat until all rows are processed. Query can be probably optimized to use only 1 temporary table.

Here is a working sqlfiddle example.

 CREATE TABLE Users
        (`id` int, `parent` int,`name` VARCHAR(10))//

    INSERT INTO Users
        (`parent`, `name`)
    VALUES  
        (1, NULL, 'root'),
        (2, 1, 'one'),
        (3, 1, '1down'),
        (4, 2, 'one_a'),
        (5, 4, 'one_a_b')//

    CREATE PROCEDURE getAncestors (in ParRowId int) 
    BEGIN 
       DECLARE tmp_parentId int;
       CREATE TEMPORARY TABLE tmp (parentId INT NOT NULL);
       CREATE TEMPORARY TABLE results (parentId INT NOT NULL);
       INSERT INTO tmp SELECT ParRowId;
       WHILE (SELECT COUNT(*) FROM tmp) > 0 DO
         SET tmp_parentId = (SELECT MIN(parentId) FROM tmp);
         DELETE FROM tmp WHERE parentId = tmp_parentId;
         INSERT INTO results SELECT parent FROM Users WHERE id = tmp_parentId AND parent IS NOT NULL;
         INSERT INTO tmp SELECT parent FROM Users WHERE id = tmp_parentId AND parent IS NOT NULL;
       END WHILE;
       SELECT * FROM Users WHERE id IN (SELECT * FROM results);
    END//

    CREATE PROCEDURE getChildren (in ParRowId int) 
    BEGIN 
       DECLARE tmp_childId int;
       CREATE TEMPORARY TABLE tmp (childId INT NOT NULL);
       CREATE TEMPORARY TABLE results (childId INT NOT NULL);
       INSERT INTO tmp SELECT ParRowId;
       WHILE (SELECT COUNT(*) FROM tmp) > 0 DO
         SET tmp_childId = (SELECT MIN(childId) FROM tmp);
         DELETE FROM tmp WHERE childId = tmp_childId;
         INSERT INTO results SELECT id FROM Users WHERE parent = tmp_childId;
         INSERT INTO tmp SELECT id FROM Users WHERE parent = tmp_childId;
       END WHILE;
       SELECT * FROM Users WHERE id IN (SELECT * FROM results);
    END//

Usage:

CALL getChildren(2);

    -- returns 
    id  parent  name
    4   2   one_a
    5   4   one_a_b


CALL getAncestors(5);

    -- returns 
    id  parent  name
    1   (null)  root
    2   1   one
    4   2   one_a