Re: a tsearch issue

On Fri, 2011-11-04 at 11:22 +0100, Pavel Stehule wrote:
> Hello
>
> I found a interesting issue when I checked a tsearch prefix searching.
>
> We use a ispell based dictionary
>
> CREATE TEXT SEARCH DICTIONARY cspell
> (template=ispell, dictfile = czech, afffile=czech, stopwords=czech);
> CREATE TEXT SEARCH CONFIGURATION cs (copy=english);
> ALTER TEXT SEARCH CONFIGURATION cs
> ALTER MAPPING FOR word, asciiword WITH cspell, simple;
>
> Then I created a table
>
> postgres=# create table n(a varchar);
> CREATE TABLE
> postgres=# insert into n values('Stěhule'),('Chromečka');
> INSERT 0 2
> postgres=# select * from n;
> a
> ───────────
> Stěhule
> Chromečka
> (2 rows)
>
> and I tested a prefix searching:
>
> I found a following issue
>
> postgres=# select * from n where to_tsvector('cs', a) @@
> to_tsquery('cs','Stě:*') ;
> a
> ───
> (0 rows)

Most likely you are hit by this problem.
http://archives.postgresql.org/pgsql-hackers/2011-10/msg01347.php

'Stě' may be a stopword in czech.

> I expected one row. The problem is in transformation of word 'Stě'
>
> postgres=# select * from ts_debug('cs','Stě:*') ;
> ─[ RECORD 1 ]┬──────────────────
> alias │ word
> description │ Word, all letters
> token │ Stě
> dictionaries │ {cspell,simple}
> dictionary │ cspell
> lexemes │ {sto}
> ─[ RECORD 2 ]┼──────────────────
> alias │ blank
> description │ Space symbols
> token │ :*
> dictionaries │ {}
> dictionary │ [null]
> lexemes │ [null]
>

':*' is only specific to to_tsquery. ts_debug just invokes the parser.
So this is not correct.

-Sushant.