INSERT INTO testDB.category_to_website (category_01_id)
SELECT t4.id
FROM testDB.websites t2
JOIN mainDB.websites t3 ON t2.url = t3.url
JOIN testDB.category_01 t4 ON t3.category2 = t4.name
WHERE t2.url = t3.url

UPDATE testDB.category_to_website
JOIN testDB.websites t2 ON t2.url = mainDB.websites.url
JOIN mainDB.websites t3 ON t2.url = t3.url
JOIN testDB.category_01 t4 ON t3.category2 = t4.name
SET t4.id=category_01_id
WHERE t2.url = t3.url

Update t4 set t4.id=t6.category_01_id from testDB.category_01 t4 as t4
 inner join  testDB.websites t2 ON t2.url = mainDB.websites.url
 inner join mainDB.websites t3 ON t2.url = t3.url
inner join testDB.category_01 t5 ON t3.category2 = t5.name
 inner join  testDB.category_to_website t6 on t4.ID=t6.category_01_id
  WHERE t2.url = t3.url