How Can MySQL Stored Procedures Solve Recursive Tree Traversal in a Bill of Materials Table?

Using MySQL Query to Traverse Rows and Create a Recursive Tree

Problem Statement

In a Bill of Materials (BOM) table with item and parent columns, you need to retrieve a recursive tree structure displaying parent-child relationships. The desired output could involve multiple levels of hierarchy, but currently, you're limited to fetching either a single level or retrieving all records and manually sorting them using a recursive function, which can be inefficient.

Solution

While MySQL itself does not natively support recursive tree traversal, you can utilize stored procedures to achieve the functionality. One approach involves creating three stored procedures:

1. GetParentIDByID: Retrieves the parent ID of a given item ID.
2. GetAncestry: Returns all the ancestors (parents and grandparents) of a given item ID.
3. GetFamilyTree: Combines the functionality of GetParentIDByID and GetAncestry to generate a complete family tree for a given item ID.

By calling these stored procedures with the starting item ID, you can recursively traverse the rows in the BOM table and construct the desired tree structure.

Example Stored Procedure:

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

Usage:

To retrieve the family tree starting from item ID 1, call the stored procedure:

CALL GetFamilyTree(1);

The result will be a comma-separated string containing the ancestry of item 1.

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