If instead of casts, functions to_tsvector() and to_tsquery() are used,
then the results is (I think ?) as expected:

select to_tsvector('simple', 'cat bat fat rat') @@ to_tsquery('simple',
'cat <-> rat');
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:t...@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;
(1 row)

regression=# select 'rat cat bat fat'::tsvector @@ 'cat <-> rat'::tsquery;
(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

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