MySQL預存程序如何解決物料清單表中的遞迴樹遍歷？

CREATE PROCEDURE GetFamilyTree(IN start_item_id INT)
BEGIN
  # Declare variables
  DECLARE parent_id INT;
  DECLARE ancestry VARCHAR(255);
  DECLARE done TINYINT DEFAULT 0;

  # Loop through item IDs until done
  WHILE NOT done DO
    # Get parent ID
    CALL GetParentIDByID(start_item_id, parent_id);

    # If parent ID is null, we're done
    IF parent_id IS NULL THEN
      SET done = 1;
      LEAVE;
    END IF;

    # Append parent ID to ancestry
    SET ancestry = CONCAT(ancestry, ',', parent_id);

    # Set current item ID to parent ID
    SET start_item_id = parent_id;
  END WHILE;

  # Return ancestry as result
  SELECT ancestry;
END

CALL GetFamilyTree(1);