You can check if a string contains another string using the position function.

> select position('One' in 'One Two Three');
 position
----------
        1

It returns the 1-based index of the first character of the first match of that substring.

> select position('Four' in 'One Two Three');
 position
----------
        0

If the substring doesn't appear within the string, then the result is 0.

Thus, you can determine if a string contains another string by checking if the value resulting from position is greater than 0.