Prefix/wildcard searches with 'websearch_to_tsquery' in PostgreSQL Full Text Search? - postgresql

Question

I'm currently using the websearch_to_tsquery function for full text search in PostgreSQL. It all works well except for the fact that I no longer seem to be able to do partial matches.
SELECT ts_headline('english', q.\"Content\", websearch_to_tsquery('english', {request.Text}), 'MaxFragments=3,MaxWords=25,MinWords=2') Highlight, *
FROM (
SELECT ts_rank_cd(f.\"SearchVector\", websearch_to_tsquery('english', {request.Text})) AS Rank, *
FROM public.\"FileExtracts\" f, websearch_to_tsquery('english', {request.Text}) as tsq
WHERE f.\"SearchVector\" ## tsq
ORDER BY rank DESC
) q
Searches for customer work but cust* and cust:* do not.
I've had a look through the documentation and a number of articles but I can't find a lot of info on it. I haven't worked with it before so hopefully it's just something simple that I'm doing wrong?

Answer 1

You can't do this with websearch_to_tsquery but you can do it with to_tsquery (because ts_query allows to add a :* wildcard) and add the websearch syntax yourself in in your backend.
For example in a node.js environment you could do smth. like this:
let trimmedSearch = req.query.search.trim()
let searchArray = trimmedSearch.split(/\s+/) //split on every whitespace and remove whitespace
let searchWithStar = searchArray.join(' & ' ) + ':*' //join word back together adds AND sign in between an star on last word
let escapedSearch = yourEscapeFunction(searchWithStar)
and than use it in your SQL
search_column ## to_tsquery('english', ${escapedSearch})

Answer 2

You need to write the tsquery directly if you want to use partial matching. plainto_tsquery doesn't pass through partial match notation either, so what were you doing before you switched to websearch_to_tsquery?
Anything that applies a stemmer is going to have hard time handling partial match. What is it supposed to do, take off the notation, stem the part, then add it back on again? Not do stemming on the whole string? Not do stemming on just the token containing the partial match indicator? And how would it even know partial match was intended, rather than just being another piece of punctuation?

Answer 3

To add something on top of the other good answers here, you can also compose your query with both websearch_to_tsquery and to_tsquery to have everything from both worlds:
select * from your_table where ts_vector_col ## to_tsquery('simple', websearch_to_tsquery('simple', 'partial query')::text || ':*')

Answer 4

Another solution I have come up with is to do the text transform as part of the query so building the tsquery looks like this
to_tsquery(concat(regexp_replace(trim(' all the search terms here '), '\W+', ':* & '), ':*'));
(trim) Removes leading/trailing whitespace
(regexp_replace) Splits the search string on non word chars and adds trailing wildcards to each term, then ANDs the terms (:* & )
(concat) Adds a trailing wildcard to the final term
(to_tsquery) Converts to a ts_query
You can test the string manipulation by running
SELECT concat(regexp_replace(trim(' all the search terms here '), '\W+', ':* & ', 'gm'), ':*')
the result should be
all:* & the:* & search:* & terms:* & here:*
So you have multi word partial matches e.g. searching spi ma would return results matching spider man