select string that doesn't contain a substring/field
I believe the problem could be summarised like this:


  Select a row from TableA if no row exists in TableB such that TableB.keyword is a substring of TableA.content.


It would probably be fair to say that the previous answer implements roughly the same logic. At the same time, it does so in a less straightforward way, in my opinion. The query below matches the proposed logic more directly and is arguably easier to follow:

SELECT
  content
FROM
  TablA
WHERE
  NOT EXISTS
  (
    SELECT
      *
    FROM
      TableB
    WHERE
      TableA.content LIKE '%' || TableB.keyword || '%'
  )
;