The IN operator cannot be used with a single field, but you can use this operator in subqueries or with predefined lists as follows:
SELECT a FROM x WHERE x.b NOT IN (SELECT b FROM y);
-- subquery is used here
SELECT a FROM x WHERE x.b NOT IN (1, 2, 3, 6);
-- predefined list is like this
But, if you are looking for the string, then go for the LIKE operator (but this will be slow) like this:
SELECT * FROM x WHERE x.a NOT LIKE '%text%';
-- It'll Find all the rows where a does not contain "text"
And if you don't want the string you are searching for then it has to start with the given string, it can also use indices (if there is an index on that field) and be reasonably fast:
SELECT * FROM x WHERE x.a NOT LIKE 'text%';
--This will find all the rows where a does not start with "text"