I'm trying to use Sphinx to find rows having words in their title column.
The query looks like this:
SELECT * FROM my_table WHERE MATCH ('#title "words"')
But it also returns rows having word (without the s) instead of words in the title.
What am I doing wrong?
Sounds like you have morphology (specifically stemming?) enabled on the index.
Should consider enabling index_exact_words
http://sphinxsearch.com/docs/current.html#conf-index-exact-words
which gives you exact form operator.
MATCH('#title =words')
Also gives you the possibility of the interesting expand_keywords option :)
http://sphinxsearch.com/docs/current.html#conf-expand-keywords
... or if dont ever want these matches, could disable stemming :) Alas there isn't a 'stemming optional' mode. (eg a ~ fuzzy operator to specifically stem)
Related
I'm using postgresql full text tsvector column.
But I found a problem:
When I search for "calça"
The results contains the following results:
1- calça red
2- calça blue
3- calçado red
Why "calçado" is being returned when I search for "calça" ?
Is there any configuration so I can solve this?
Thanks.
It isn't just a matter that one string contains the other. The Portuguese stemmer thinks this is the way they should be stemmed. If you turn the longer word into 'calçadot', for example, it no longer stems it, because (presumably) 'adot' is not recognized as a Portuguese suffix which ought to be removed the way 'ado' is.
If you don't want stemming at all, then you could change the config to 'simple', which doesn't stem. But at that point, maybe you don't want full text search at all, and could just use LIKE instead with a pg_trgm index.
If it is just this particular word that you don't want stemmed, I think you can set up a synonym dictionary which will map calçado to itself, which will bypass stemming.
I was experimenting with PostgreSQL's text search feature - particularly with the normalization function to_tsquery.
I was using english dictionary(config) and for some reason s and t won't normalize. I understand why i and a would not, but s and t? Interesting.
Are they matched to single space and tab?
Here is the query:
select
to_tsquery('english', 'a:*') as for_a,
to_tsquery('english', 's:*') as for_s,
to_tsquery('english', 't:*') as for_t,
to_tsquery('english', 'u:*') as for_u
fiddle just in case.
You would see 'u:*' is returning as 'u:*' and 'a:*' is not returning anything.
The letters s and t are considered stop words in the english text search dictionary, therefore they get discarded. You can read the stop word list under tsearch_data/english.stop in the postgres shared folder, which you can locate by typing pg_config --sharedir
With pg 11 on ubuntu/debian/mint, that would be
cat /usr/share/postgresql/11/tsearch_data/english.stop
Quoting from the docs,
Stop words are words that are very common, appear in almost every document, and have no discrimination value. Therefore, they can be ignored in the context of full text searching.
It is best to discard english grammar and think of words in a programmatic and logical way as described above. Full text search does not try to infer context based on sentence structuring so it has no use for these words. After all, it's called full text search and not natural language search.
As to how they arrived on the conclusion to add s and t to the stop word list, statistical analysis must have revealed these characters to be noise.
I am trying to search for multiple words in text inclusively(AND operation)
without losing word stemming.
For example:
db.supplies.runCommand("text", {search:"printers inks"})
should return results with (printer and ink) or (printers ink) or (printers ink) or (printers inks) , instead of all results with either printer or ink.
This post covers the search for multiple words as an AND operation, but the solution doesn't search for stemmed words ->MongoDB Text Search AND multiple search words.
The only way I could think of is creating a permutation of all the words and then running the search for the number of permutations(which could be large)
This may not be an effective way to search on a large collection.
Is there a better and smarter way to do it ?
So is there a reason you have to use a text search? If it were me i would use a regular expression.
https://docs.mongodb.com/manual/reference/operator/query/regex/
Off the top of my head something like this.
db.collection.find({products:/printers inks|printers|inks/})
Now i suppose you can do the same thing with a text search too.
db.collection.find({$text:{$search : "\"printers inks\" printers inks"}})
note the escaped quotes.
I have an app that utilizes hashtags to help tag posts. I am trying to have a more detailed search.
Lets say one of the records I'm searching is:
The #bird flew very far.
When I search for "flew", "fle", or "#bird", it should return the record.
However, when I search "#bir", it should NOT return the sentence because the whole the tag being searched for doesn't match.
I'm also not sure if "bird" should even return the sentence. I'd be interested how to do that though as well.
Right now, I have a very basic search:
SELECT "posts".* FROM "posts" WHERE (body LIKE '%search%')
Any ideas?
You could do this with LIKE but it would be rather hideous, regexes will serve you better here. If you want to ignore the hashes then a simple search like this will do the trick:
WHERE body ~ E'\\mbird\M''
That would find 'The bird flew very far.' and 'The #bird flew very far.'. You'd want to strip off any #s before search though as this:
WHERE body ~ E'\\m#bird\M''
wouldn't find either of those results due to the nature of \m and \M.
If you don't want to ignore #s in body then you'd have to expand and modify the \m and \M shortcuts yourself with something like this:
WHERE body ~ E'(^|[^\\w#])#bird($|[^\\w#])'
-- search term goes here^^^^^
Using E'(^|[^\\w#])#bird($|[^\\w#])' would find 'The #bird flew very far.' but not 'The bird flew very far.' whereas E'(^|[^\\w#])bird($|[^\\w#])' would find 'The bird flew very far.' but not 'The #bird flew very far.'. You might also want to look at \A instead of ^ and \Z instead of $ as there are subtle differences but I think $ and ^ would be what you want.
You should keep in mind that none of these regex searches (or your LIKE search for that matter) will uses indexes so you're setting yourself up for lots of table scans and performance problems unless you can restrict the searches using something that will use an index. You might want to look at a full-text search solution instead.
It might help to parse the hash tags out of the text and store them in an array in a separate column called say hashtags when the articles are inserted/updated. Remove them from the article body before feeding it into to_tsvector and store the tsvector in a column of the table. Then use:
WHERE body_tsvector ## to_tsquery('search') OR 'search' IN hashtags
You could use a trigger on the table to maintain the hashtags column and the body_tsvector stripped of hash tags, so that the application doesn't have to do the work. Parse them out of the text when entries are INSERTed or UPDATEd.
For example, searching for the word cat, I would want to match words with #*cat*. I already have the hash tag indexing setup, and I have sphinx setup for star searches.
Its not well documented and I've never tried it myself, but a post here:
http://sphinxsearch.com/forum/view.html?id=9847
from a Sphinx developer, suggests that using a plain index, and dict=keywords, would allow wildcard, so could search
#%cat*
For some reason % seems to be used as the wildcard in the middle of a string.