Re: Full Text Search combined with Fuzzy

On 03.03.2017 15:49, Nicolas Paris wrote:
>
> Hi Oleg,
>
> Thanks. I thought pgtrgm was not able to index my long texts because of
> limitation of 8191 bytes per index row for btree.
>
> Then I found out it is possible to use pgtrgm over a GIN/GIST index.
> My final use case is phrase mining in texts.
>
> I want my application returns texts that contains approximatly the user
> entry:
>
> Eg: user search "Hello Word"
> a text containing "blah blah blah hello world blah blah blah" would be
> returned.
>
> Test:
> postgres=# CREATE table test_trgm (texts text);
> CREATE TABLE
> postgres=# CREATE INDEX ON test_trgm USING GIN(texts gin_trgm_ops);
> CREATE INDEX
> postgres=# SET enable_seqscan = OFF;
> SET
> postgres=# insert into test_trgm VALUES ('blah blah blah hello world blah blah blah');
> INSERT 0 1
> postgres=# insert into test_trgm VALUES ('blah blah blah hello word blah blah blah');
> INSERT 0 1
> postgres=# SELECT texts, similarity(texts, 'hello word') FROM test_trgm WHERE texts % 'hello word';
> texts | similarity
> -------------------------------------------+------------
> blah blah blah hello world blah blah blah | 0.473684
> blah blah blah hello word blah blah blah | 0.6875
> (2 rows)
>
> postgres=# EXPLAIN SELECT texts, similarity(texts, 'hello word') FROM test_trgm WHERE texts % 'hello word';
> QUERY PLAN
> -----------------------------------------------------------------------------------
> Bitmap Heap Scan on test_trgm (cost=52.01..56.03 rows=1 width=32)
> Recheck Cond: (texts % 'hello word'::text)
> -> Bitmap Index Scan on test_trgm_texts_idx (cost=0.00..52.01 rows=1 width=0)
> Index Cond: (texts % 'hello word'::text)
> (4 rows)
>
> Conclusion: If I d'say 0.4 is my threshold, would this methodology meet
> my requirements ?
>
> Thanks for the help !
>

Hello,

If you use PostgreSQL 9.6, then word_similarity() can help you [1]. For
example:

postgres=# SELECT texts, word_similarity('hello word', texts) FROM
test_trgm WHERE 'hello word' <% texts;
texts | word_similarity
-------------------------------------------+-----------------
blah blah blah hello world blah blah blah | 0.818182
blah blah blah hello word blah blah blah | 1
(2 rows)

1. https://www.postgresql.org/docs/9.6/static/pgtrgm.html

--
Artur Zakirov
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Russian Postgres Company