Re: Rethinking our fulltext phrase-search implementation

Hello Tom,

On 17.12.2016 21:36, Tom Lane wrote:
>
> 4. The transformations are wrong anyway. The OR case I showed above is
> all right, but as I argued in <24331(dot)1480199636(at)sss(dot)pgh(dot)pa(dot)us>, the AND
> case is not:
>
> regression=# select 'a <-> (b & c)'::tsquery;
> tsquery
> ---------------------------
> 'a' <-> 'b' & 'a' <-> 'c'
> (1 row)
>
> This matches 'a b a c', because 'a <-> b' and 'a <-> c' can each be
> matched at different places in that text; but it seems highly unlikely to
> me that that's what the writer of such a query wanted. (If she did want
> that, she would write it that way to start with.) NOT is not very nice
> either:

If I'm not mistaken PostgreSQL 9.6 and master with patch
"fix-phrase-search.patch" return false for the query:

select 'a b a c' @@ 'a <-> (b & c)'::tsquery;
?column?
----------
f
(1 row)

I agree that such query is confusing. Maybe it is better to return true
for such queries?
Otherwise it seems that queries like 'a <-> (b & c)' will always return
false. Then we need maybe some warning message.

--
Artur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company