On Wed, Jun 8, 2016 at 9:01 PM, Jean-Pierre Pelletier
<jppelletier@e-djuster.com> wrote:
> If instead of casts, functions to_tsvector() and to_tsquery() are used,
> then the results is (I think ?) as expected:
because to_tsvector() function returns positions of words.
>
> select to_tsvector('simple', 'cat bat fat rat') @@ to_tsquery('simple',
> 'cat <-> rat');
> or
> select to_tsvector('simple', 'rat cat bat fat') @@ to_tsquery('simple',
> 'cat <-> rat');
> returns "false"
>
> select to_tsvector('simple', 'cat rat bat fat') @@ to_tsquery('simple',
> 'cat <-> rat');
> returns "true"
>
> Jean-Pierre Pelletier
>
> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> Sent: Wednesday, June 8, 2016 1:12 PM
> To: Teodor Sigaev; Oleg Bartunov
> Cc: Jean-Pierre Pelletier; pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] Should phraseto_tsquery('simple', 'blue blue') @@
> to_tsvector('simple', 'blue') be true ?
>
> Another thing I noticed: if you test with tsvectors that don't contain
> position info, <-> seems to reduce to &, that is it doesn't enforce
> relative position:
>
> regression=# select 'cat bat fat rat'::tsvector @@ 'cat <-> rat'::tsquery;
> ?column?
> ----------
> t
> (1 row)
>
> regression=# select 'rat cat bat fat'::tsvector @@ 'cat <-> rat'::tsquery;
> ?column?
> ----------
> t
> (1 row)
>
> I'm doubtful that this is a good behavior, because it seems like it can
> silently mask mistakes. That is, applying <-> to a stripped tsvector
> seems like user error to me. Actually throwing an error might be too
> much, but perhaps we should make such cases return false not true?
>
> (This is against HEAD, without the patch I suggested yesterday.
> It strikes me that that patch might change this behavior, if the lexemes
> are all being treated as having position zero, but I have not checked.)
>
> regards, tom lane