SQL Substring in WHERE clause
You need t o compare product.info with descriptions.info. If the needed condition is for one to be a substring of the other, it can be done with LIKE.

Since there may be more than one descriptions matching (having as substring) a product code, we should use an EXISTS subquery:

SELECT p.id, p.code
FROM products AS p
WHERE p.description IS NULL
  AND EXISTS
      ( SELECT *
        FROM descriptions AS d 
        WHERE d.info LIKE '%' + p.code + '%'
      ) ;