Retrieve top-level parent MySQL

Question

I have the following table:

  id  |  parent_id  |  searchable  |  value
--------------------------------------------
  1   |      0      |      0       |    a
           


        

Answer 1

You will have to use stored procedure to do it.

Find all rows with searchable = 1, store their ids and parent_ids in a temp table. Then do self-joins to add parents to this temp table. Repeat until no more rows can be added (obviously better make sure tree is not cyclic). At the end you have a table only with rows that have a searchable descendant somewhere down the tree, so just show only rows with no parent (at the top).

Assuming your table is called 'my_table' this one should work:

DELIMITER //
DROP PROCEDURE IF EXISTS top_level_parents//
CREATE PROCEDURE top_level_parents()
BEGIN
  DECLARE found INT(11) DEFAULT 1;
  DROP TABLE IF EXISTS parent_tree;
  CREATE TABLE parent_tree (id int(11) PRIMARY KEY, p_id int(11)) ENGINE=HEAP;
  INSERT INTO parent_tree
    SELECT id, parent_id FROM my_table
    WHERE searchable = 1;
  SET found = ROW_COUNT();
  WHILE found > 0 DO
    INSERT IGNORE INTO parent_tree
      SELECT p.id, p.parent_id FROM parent_tree c JOIN my_table p
      WHERE p.id = c.p_id;
    SET found = ROW_COUNT();
  END WHILE;
  SELECT id FROM parent_tree WHERE p_id = 0;
  DROP TABLE parent_tree;
END;//
DELIMITER ;

Then just calling it:

CALL top_level_parents();

will be equal to SELECT id FROM my_table WHERE id_is_top_level_and_has_searchable_descendant