Find a strict string in a field

I have a database, which contains a field 'topic'. This field is a short text, about 200-300 words, I would say.

I need to find a string in this field, but in a particular way: only the string, and nothing else. Such things as

SELECT * FROM table WHERE abstract like '%myString%"

Are not possible, because it would also return something+my_string+something.

SELECT * FROM table WHERE abstract like '_myString_"

Does not work either, because my field could start with myString, and it would not match.

I would love to use REGEXP, but sqlite doesn't seem to support it yet. I read it is possible to tweak it, and use a personal function, but I would need a way to implement it for PyQt, to use it in my application.

Do you have any idea ?