Message-ID: <c58ac11e7fe0c11d84b3e5fb3244a434d8d87509.camel@cybertec.at>
Subject: Re: Functions and Indexes
From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Moreno Andreo <moreno.andreo@evolu-s.it>, 
	pgsql-general@lists.postgresql.org
Date: Tue, 19 Nov 2024 12:34:03 +0100
In-Reply-To: <14fa809c-a2b7-4d36-9382-d08a5df4718a@evolu-s.it>
References: <2e36a2fe-b30f-46a5-937f-3b7d94e75cb6@evolu-s.it>
	 <8dfd0bd5-87e5-4de7-9f60-8a680a32bc11@evolu-s.it>
	 <61cb94a962667788c9c09107fa9937300e54d3cd.camel@cybertec.at>
	 <14fa809c-a2b7-4d36-9382-d08a5df4718a@evolu-s.it>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.52.4 (3.52.4-2.fc40) 
MIME-Version: 1.0
Archived-At: <https://www.postgresql.org/message-id/c58ac11e7fe0c11d84b3e5fb3244a434d8d87509.camel%40cybertec.at>
Precedence: bulk

On Tue, 2024-11-19 at 11:53 +0100, Moreno Andreo wrote:
> > > What about if query becomes
> > > SELECT foo1, foo2 FROM bar WHERE (POSITION(foo1 IN 'blah blah') >0)
> >
> > You could create an index like
> >=20
> > =C2=A0=C2=A0=C2=A0 CREATE INDEX ON bar (position(foo1 IN 'blah blah'));
> >=20
> > Alternatively, you could have a partial index:
> >=20
> > =C2=A0=C2=A0=C2=A0 CREATE INDEX ON bar (foo1) INCLUDE (foo2)
> > =C2=A0=C2=A0=C2=A0 WHERE position(foo1 IN 'blah blah') > 0;
>
> Interesting. Never seen this form, I'll look further on it.
>=20
> I stumbled into
> https://www.cybertec-postgresql.com/en/indexing-like-postgresql-oracle/
> and discovered text_pattern_ops.
> I'm wondering if it can be of any use in my index, that should hold a=20
> WHERE condition with a combination of LIKE and the POSITION expression=
=20
> above.
> More docs to read ... :-)

I don't think "text_pattern_ops" will help here - queries that use LIKE
to search for a substring (LIKE '%string%') cannot make use of a b-tree
index.

Yours,
Laurenz Albe