Need Help with Hierarchical Mysql Query

Question

I\'m trying to wrap my head around querying a table that has hierarchical category data (used for a cms) which is also tied to my posts data and a many-to-many type relation

Answer 1

There are perhaps better methods, but here's an idea:

CREATE VIEW subcategories AS
( SELECT 0        AS level
       , cat_0.id AS cat_id
       , cat_0.id AS subcat_id
  FROM categories cat_0

  UNION ALL

  SELECT 1        AS level
       , cat_0.id AS cat_id
       , cat_1.id AS subcat_id
  FROM categories cat_0
    JOIN categories cat_1
      ON cat_0.id = cat_1.parent_id

  UNION ALL

  SELECT 2        AS level
       , cat_0.id AS cat_id
       , cat_2.id AS subcat_id
  FROM categories cat_0
    JOIN categories cat_1
      ON cat_0.id = cat_1.parent_id
    JOIN categories cat_2
      ON cat_1.id = cat_2.parent_id

  UNION ALL

  SELECT 3        AS level
       , cat_0.id AS cat_id
       , cat_3.id AS subcat_id
  FROM categories cat_0
    JOIN categories cat_1
      ON cat_0.id = cat_1.parent_id
    JOIN categories cat_2
      ON cat_1.id = cat_2.parent_id
    JOIN categories cat_3
      ON cat_2.id = cat_3.parent_id
) ;

Then, use the above to have:

SELECT sub.subcat_id
     , sub.level
     , p.post_id
     , p.title
FROM subcategories sub
  JOIN post2cat p2c
    ON sub.subcat_id = p2c.cat_id
  JOIN posts p
    ON p2c.post_id = p.id
WHERE sub.cat_id = CAT_ID        <--- the category id you want to search for