模糊搜索与全文搜索有什么区别？

Question

In my project, I am asked to implement a text query service on the database we are using; Postgresql. I have used Postgresql Full Text Search features, which works fairly fine in terms of time. One problem about full text search is, it does not have fuzzy search abilities. On the other hand, there is an extension named pgtrgm providing functions and operators for determining the similarity of alphanumeric text . Also there are several examples of text search using pgtrgm like:

select actor
    from products
    where actor % 'tomy';

As you know example of postgres FTS also here;

SELECT title
FROM pgweb
WHERE to_tsvector(body) @@ to_tsquery('friend');

So, the main question is, what is the difference between these two search strategies? Which one is more appropriate way for searching texts? Is it possible to mix them? I also need to say that performance is an important concern as well. Thanks in advance!

Answer 1

They do completely different things. About the only thing that is not different between them is that they operate on text and can benefit from use of indexes. From you question, it seems like you already have a good sense of the differences. The appropriate one is the one that does what you want. If one of them was always appropriate, we probably wouldn't have created the other one.

You can mix them, but you will need different indexes for each one, they cannot share an index. Also, you probably need different tables as well, as full text search is more appropriate for sentences or paragraphs while trigram for individual words or short phrases.

One way to mix them would be to have one table of full texts, and another table which lists only each distinct word present in any of the full texts. The 2nd table could be used to detect probable typos in the query, and then once those are fixed by suggestions from trigram searching, run the fixed query against the 1st table.

Answer 2

The difference is quite huge - in fuzzy search, you're searching for a similar result, in full-text search - for the exact same. If one is more appropriate than the other is the matter of use-case.

If you don't need fuzziness, don't use it, it's a huge performance overhead because it has to match the text not exactly, but also try other combinations.