Re: Precedence of new phrase search tsquery operator

On Wed, Jun 8, 2016 at 7:13 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> It appears that the new <-> operator has been made to have exactly the
> same grammatical precedence as the existing & (AND) operator. Thus,
> for example, 'a & b <-> c'::tsquery means something different from
> 'b <-> c & a'::tsquery:
>
> regression=# select 'a & b <-> c'::tsquery;
> tsquery
> -----------------------------------
> ( 'a' <-> 'c' ) & ( 'b' <-> 'c' )
> (1 row)
>
> regression=# select 'b <-> c & a'::tsquery;
> tsquery
> -----------------------
> ( 'b' <-> 'c' ) & 'a'
> (1 row)
>
> I find this surprising. My intuitive feeling is that <-> ought to
> bind tighter than & (and therefore also tighter than |). What's
> the reasoning for making it act like this?

I don't remember, but it looks like a bug. I found another issue with that

If some dictionary returns two infinitives, like:

select * from to_tsquery('en','leavings');
to_tsquery
----------------------
'leavings' | 'leave'
(1 row)

then following query looks like a bug

select to_tsquery('en', 'aa & leavings <-> tut');
to_tsquery
-------------------------------------------------------------------
( 'aa' <-> 'tut' ) & ( 'leavings' <-> 'tut' | 'leave' <-> 'tut' )
(1 row)

It should be definitely

select to_tsquery('en', 'aa & leavings <-> tut');
to_tsquery
-------------------------------------------------------------------
'aa' & ( 'leavings' <-> 'tut' | 'leave' <-> 'tut' )
(1 row)

so, yes, <-> should be more tight than &.

>
> regards, tom lane