Weird ranking results with ts_rank
Hi everybody.
I'm implementing a solution that uses PostgreSQL's full text search
capabilities and I have come across a particular set of results for ts_rank
that don't seem to make sense according to the documentation. I have tried
the following queries in PostgreSQL 10, 11 and 12.
In both cases only the word "box" is matching, but adding a non-matching
word with OR to the query increases the ranking. If I keep adding more
non-matching words with OR the ranking starts to decrease again, but I
would imagine that the second option should have the highest score and it
would start decreasing from there the more non-matching words I add.
Is there something I'm not understanding?
Thanks.
postgres=# select ts_rank(to_tsvector('search for a text box'),
to_tsquery('circle | lot <-> box'));
ts_rank
-
0.020264236
(1 row)
postgres=# select ts_rank(to_tsvector('search for a text box'),
to_tsquery('lot <-> box'));
ts_rank
-
1e-20
(1 row)
--
Javier Ayres
Data Engineer
+1 855 636 5811 <+18556365811> - sophilabs.co
Re: Weird ranking results with ts_rank
Oh I see. I was working as if no match was the same as ts_rank=0.
Great advice. Thank you very much.
On Sat, Nov 16, 2019 at 2:22 PM Jeff Janes wrote:
> On Fri, Nov 15, 2019 at 1:31 AM Javier Ayres wrote:
>
>> Hi everybody.
>>
>> I'm implementing a solution that uses PostgreSQL's full text search
>> capabilities and I have come across a particular set of results for ts_rank
>> that don't seem to make sense according to the documentation.
>>
>
> While the documentation doesn't come out and say, my interpretation is
> that ts_rank assumes there is a match in the first place, and by
> implication is undefined/unspecified if there is no match.
>
> select to_tsvector('search for a text box') @@ to_tsquery('circle | lot
> <-> box');
> ?column?
> --
> f
> (1 row)
>
> Cheers,
>
> Jeff
>
--
Javier Ayres
Data Engineer
+1 855 636 5811 <+18556365811> - sophilabs.co
