MySQL - Recursing a tree structure

Question

I have a database table which link locations together; a location can be in a location, which can be inside another location.

location (, ....)
loc         


        

Answer 1

This is an old question, but since i stumbled over this searching for a solution.

Since MySQL 8.0, you can use a recursive CTE for this:

WITH RECURSIVE tmp (id) AS
(
  SELECT id
    FROM locations
    WHERE parent_id IS NULL
  UNION ALL
  SELECT l.id
    FROM tmp AS p JOIN locations AS l
      ON p.id = l.parent_id
)
SELECT * FROM tmp
ORDER BY id;

This assumes a slightly different DB structure than in the original question (eg. there is only one table containing both parents/children), however, I am sure that this technique applies there as well.