Re: Can pg_trgm handle non-alphanumeric characters?
От | MauMau |
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Тема | Re: Can pg_trgm handle non-alphanumeric characters? |
Дата | |
Msg-id | DD0DD117F67E48E5961C326E5C050A3E@maumau обсуждение исходный текст |
Ответ на | Re: Can pg_trgm handle non-alphanumeric characters? ("Kevin Grittner" <Kevin.Grittner@wicourts.gov>) |
Ответы |
Re: Can pg_trgm handle non-alphanumeric characters?
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Список | pgsql-hackers |
From: "Kevin Grittner" <Kevin.Grittner@wicourts.gov> > "MauMau" <maumau307@gmail.com> wrote: >> For information, what kind of breakage would occur? > >> I imagined removing KEEPONLYALNUM would just accept >> non-alphanumeric characters and cause no harm to those who use >> only alphanumeric characters. > > This would break our current usages because of the handling of > trigrams at the "edges" of groups of qualifying characters. It > would make similarity (and distance) values less useful for our > current name searches using it. To simulate the effect, I used an > '8' in place of a comma instead of recompiling with the suggested > change. > > test=# select show_trgm('smith,john'); > show_trgm > ----------------------------------------------------------- > {" j"," s"," jo"," sm","hn ",ith,joh,mit,ohn,smi,"th "} > (1 row) > > test=# select show_trgm('smith8john'); > show_trgm > ----------------------------------------------------- > {" s"," sm",8jo,h8j,"hn ",ith,joh,mit,ohn,smi,th8} > (1 row) > > test=# select similarity('smith,john', 'jon smith'); > similarity > ------------ > 0.615385 > (1 row) > > test=# select similarity('smith8john', 'jon smith'); > similarity > ------------ > 0.3125 > (1 row) > > So making the proposed change unconditionally could indeed hurt > current users of the technique. On the other hand, if there was > fine-grained control of this, it might make trigrams useful for > searching statute cites (using all characters) as well as names > (using the current character set); so I wouldn't want it to just be > controlled by a global GUC. Thanks for your explanation. Although I haven't understood it well yet, I'll consider what you taught. And I'll consider if the tentative measure of removing KEEPONLYALNUM is correct for someone who wants to use pg_trgm against Japanese text. Regards MauMau
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