pg.ddx.io pgsql-performance@postgresql.org mailing list archive
help / color / mirror / Atom feedLIKE query on indexes
9+ messages / 5 participants
[nested] [flat]
* LIKE query on indexes
@ 2006-02-21 15:57 Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 17:40 ` Re: LIKE query on indexes mark@mark.mielke.cc
0 siblings, 2 replies; 9+ messages in thread
From: Ibrahim Tekin @ 2006-02-21 15:57 UTC (permalink / raw)
To: pgsql-performance
hi,
i have btree index on a text type field. i want see rows which starts with
certain characters on that field. so i write a query like this:
SELECT * FROM mytable WHERE myfield LIKE 'john%'
since this condition is from start of the field, query planner should use
index to find such elements but explain command shows me it will do a
sequential scan.
is this lack of a feature or i am wrong somewhere?
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
@ 2006-02-21 16:18 ` Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 16:34 ` Re: LIKE query on indexes Alvaro Herrera <alvherre@commandprompt.com>
1 sibling, 1 reply; 9+ messages in thread
From: Scott Marlowe @ 2006-02-21 16:18 UTC (permalink / raw)
To: Ibrahim Tekin <itekin@gmail.com>; +Cc: pgsql-performance
On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> hi,
> i have btree index on a text type field. i want see rows which starts
> with certain characters on that field. so i write a query like this:
>
> SELECT * FROM mytable WHERE myfield LIKE 'john%'
>
> since this condition is from start of the field, query planner should
> use index to find such elements but explain command shows me it will
> do a sequential scan.
>
> is this lack of a feature or i am wrong somewhere?
This is an artifact of how PostgreSQL handles locales other than ASCII.
If you want such a query to use an index, you need to back up your
database, and re-initdb with --locale=C as an argument. Note that you
then will NOT get locale specific matching and sorting.
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
@ 2006-02-21 16:34 ` Alvaro Herrera <alvherre@commandprompt.com>
2006-02-21 16:42 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 20:28 ` Re: LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
0 siblings, 2 replies; 9+ messages in thread
From: Alvaro Herrera @ 2006-02-21 16:34 UTC (permalink / raw)
To: Scott Marlowe <smarlowe@g2switchworks.com>; +Cc: Ibrahim Tekin <itekin@gmail.com>; pgsql-performance
Scott Marlowe wrote:
> On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> > hi,
> > i have btree index on a text type field. i want see rows which starts
> > with certain characters on that field. so i write a query like this:
> >
> > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> >
> > since this condition is from start of the field, query planner should
> > use index to find such elements but explain command shows me it will
> > do a sequential scan.
> >
> > is this lack of a feature or i am wrong somewhere?
>
> This is an artifact of how PostgreSQL handles locales other than ASCII.
>
> If you want such a query to use an index, you need to back up your
> database, and re-initdb with --locale=C as an argument.
... or you can choose to create an index with the text_pattern_ops
operator class, which would be used in a LIKE constraint regardless of
locale.
http://www.postgresql.org/docs/8.1/static/indexes-opclass.html
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 16:34 ` Re: LIKE query on indexes Alvaro Herrera <alvherre@commandprompt.com>
@ 2006-02-21 16:42 ` Scott Marlowe <smarlowe@g2switchworks.com>
1 sibling, 0 replies; 9+ messages in thread
From: Scott Marlowe @ 2006-02-21 16:42 UTC (permalink / raw)
To: Alvaro Herrera <alvherre@commandprompt.com>; +Cc: Ibrahim Tekin <itekin@gmail.com>; pgsql-performance
On Tue, 2006-02-21 at 10:34, Alvaro Herrera wrote:
> Scott Marlowe wrote:
> > On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> > > hi,
> > > i have btree index on a text type field. i want see rows which starts
> > > with certain characters on that field. so i write a query like this:
> > >
> > > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> > >
> > > since this condition is from start of the field, query planner should
> > > use index to find such elements but explain command shows me it will
> > > do a sequential scan.
> > >
> > > is this lack of a feature or i am wrong somewhere?
> >
> > This is an artifact of how PostgreSQL handles locales other than ASCII.
> >
> > If you want such a query to use an index, you need to back up your
> > database, and re-initdb with --locale=C as an argument.
>
> ... or you can choose to create an index with the text_pattern_ops
> operator class, which would be used in a LIKE constraint regardless of
> locale.
>
> http://www.postgresql.org/docs/8.1/static/indexes-opclass.html
Good point. I tend to view the world from the perspective of the 7.4
and before user...
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 16:34 ` Re: LIKE query on indexes Alvaro Herrera <alvherre@commandprompt.com>
@ 2006-02-21 20:28 ` Ibrahim Tekin <itekin@gmail.com>
2006-02-22 15:48 ` Re: LIKE query on indexes Brendan Duddridge <brendan@clickspace.com>
1 sibling, 1 reply; 9+ messages in thread
From: Ibrahim Tekin @ 2006-02-21 20:28 UTC (permalink / raw)
To: Scott Marlowe <smarlowe@g2switchworks.com>; Ibrahim Tekin <itekin@gmail.com>; pgsql-performance
this trick did the job.
thanks.
On 2/21/06, Alvaro Herrera <alvherre@commandprompt.com> wrote:
>
> Scott Marlowe wrote:
> > On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> > > hi,
> > > i have btree index on a text type field. i want see rows which starts
> > > with certain characters on that field. so i write a query like this:
> > >
> > > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> > >
> > > since this condition is from start of the field, query planner should
> > > use index to find such elements but explain command shows me it will
> > > do a sequential scan.
> > >
> > > is this lack of a feature or i am wrong somewhere?
> >
> > This is an artifact of how PostgreSQL handles locales other than ASCII.
> >
> > If you want such a query to use an index, you need to back up your
> > database, and re-initdb with --locale=C as an argument.
>
> ... or you can choose to create an index with the text_pattern_ops
> operator class, which would be used in a LIKE constraint regardless of
> locale.
>
> http://www.postgresql.org/docs/8.1/static/indexes-opclass.html
>
> --
> Alvaro Herrera
> http://www.CommandPrompt.com/
> The PostgreSQL Company - Command Prompt, Inc.
>
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 16:34 ` Re: LIKE query on indexes Alvaro Herrera <alvherre@commandprompt.com>
2006-02-21 20:28 ` Re: LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
@ 2006-02-22 15:48 ` Brendan Duddridge <brendan@clickspace.com>
2006-02-23 12:52 ` Re: LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
0 siblings, 1 reply; 9+ messages in thread
From: Brendan Duddridge @ 2006-02-22 15:48 UTC (permalink / raw)
To: Ibrahim Tekin <itekin@gmail.com>; +Cc: Scott Marlowe <smarlowe@g2switchworks.com>; pgsql-performance
Hi,
Can this technique work with case insensitive ILIKE?
It didn't seem to use the index when I used ILIKE instead of LIKE.
Thanks,
____________________________________________________________________
Brendan Duddridge | CTO | 403-277-5591 x24 | brendan@clickspace.com
ClickSpace Interactive Inc.
Suite L100, 239 - 10th Ave. SE
Calgary, AB T2G 0V9
http://www.clickspace.com
On Feb 21, 2006, at 1:28 PM, Ibrahim Tekin wrote:
> this trick did the job.
> thanks.
>
> On 2/21/06, Alvaro Herrera <alvherre@commandprompt.com> wrote:
> Scott Marlowe wrote:
> > On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> > > hi,
> > > i have btree index on a text type field. i want see rows which
> starts
> > > with certain characters on that field. so i write a query like
> this:
> > >
> > > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> > >
> > > since this condition is from start of the field, query planner
> should
> > > use index to find such elements but explain command shows me it
> will
> > > do a sequential scan.
> > >
> > > is this lack of a feature or i am wrong somewhere?
> >
> > This is an artifact of how PostgreSQL handles locales other than
> ASCII.
> >
> > If you want such a query to use an index, you need to back up your
> > database, and re-initdb with --locale=C as an argument.
>
> ... or you can choose to create an index with the text_pattern_ops
> operator class, which would be used in a LIKE constraint regardless of
> locale.
>
> http://www.postgresql.org/docs/8.1/static/indexes-opclass.html
>
> --
> Alvaro Herrera http://
> www.CommandPrompt.com/
> The PostgreSQL Company - Command Prompt, Inc.
>
Attachments:
smime.p7s (application/pkcs7-signature, 2.3K) download
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Re: LIKE query on indexes Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 16:34 ` Re: LIKE query on indexes Alvaro Herrera <alvherre@commandprompt.com>
2006-02-21 20:28 ` Re: LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-22 15:48 ` Re: LIKE query on indexes Brendan Duddridge <brendan@clickspace.com>
@ 2006-02-23 12:52 ` Ibrahim Tekin <itekin@gmail.com>
0 siblings, 0 replies; 9+ messages in thread
From: Ibrahim Tekin @ 2006-02-23 12:52 UTC (permalink / raw)
To: Brendan Duddridge <brendan@clickspace.com>; +Cc: Scott Marlowe <smarlowe@g2switchworks.com>; pgsql-performance
hi,
i ran a query with ILIKE but it doesn't use the index.
but i tried following method, and it worked. there is 3 extra lower()
overhead but i don't think it will effect the performance.
CREATE INDEX index_name ON mytable (lower(column) varchar_pattern_ops);
SELECT * FROM mytable WHERE lower(column) LIKE lower('beginswith%')
if insert operations are high in database. you use only this index to search
case sensitive.
say you want this:
SELECT * FROM mytable WHERE column LIKE 'beGinsWith%'
write this:
SELECT * FROM mytable WHERE lower(column) LIKE lower('beGinsWith%') AND
column LIKE 'beGinsWith%'
than query planner will search on index, than scan the resulting bitmap
heap.
On 2/22/06, Brendan Duddridge <brendan@clickspace.com> wrote:
>
> Hi,
> Can this technique work with case insensitive ILIKE?
>
> It didn't seem to use the index when I used ILIKE instead of LIKE.
> Thanks,
> *
> *____________________________________________________________________
> *Brendan Duddridge* | CTO | 403-277-5591 x24 | brendan@clickspace.com
> *
> *ClickSpace Interactive Inc.
> Suite L100, 239 - 10th Ave. SE
> Calgary, AB T2G 0V9
>
> http://www.clickspace.com
>
> On Feb 21, 2006, at 1:28 PM, Ibrahim Tekin wrote:
>
> this trick did the job.
> thanks.
>
> On 2/21/06, Alvaro Herrera <alvherre@commandprompt.com> wrote:
> >
> > Scott Marlowe wrote:
> > > On Tue, 2006-02-21 at 09:57, Ibrahim Tekin wrote:
> > > > hi,
> > > > i have btree index on a text type field. i want see rows which
> > starts
> > > > with certain characters on that field. so i write a query like this:
> > > >
> > > > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> > > >
> > > > since this condition is from start of the field, query planner
> > should
> > > > use index to find such elements but explain command shows me it will
> > > > do a sequential scan.
> > > >
> > > > is this lack of a feature or i am wrong somewhere?
> > >
> > > This is an artifact of how PostgreSQL handles locales other than
> > ASCII.
> > >
> > > If you want such a query to use an index, you need to back up your
> > > database, and re-initdb with --locale=C as an argument.
> >
> > ... or you can choose to create an index with the text_pattern_ops
> > operator class, which would be used in a LIKE constraint regardless of
> > locale.
> >
> > http://www.postgresql.org/docs/8.1/static/indexes-opclass.html
> >
> > --
> > Alvaro Herrera http://www.CommandPrompt.com/
> > The PostgreSQL Company - Command Prompt, Inc.
> >
>
>
>
>
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
@ 2006-02-21 17:40 ` mark@mark.mielke.cc
2006-02-21 20:12 ` Re: LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
1 sibling, 1 reply; 9+ messages in thread
From: mark@mark.mielke.cc @ 2006-02-21 17:40 UTC (permalink / raw)
To: Ibrahim Tekin <itekin@gmail.com>; +Cc: pgsql-performance
On Tue, Feb 21, 2006 at 05:57:12PM +0200, Ibrahim Tekin wrote:
> i have btree index on a text type field. i want see rows which starts with
> certain characters on that field. so i write a query like this:
> SELECT * FROM mytable WHERE myfield LIKE 'john%'
> since this condition is from start of the field, query planner should use
> index to find such elements but explain command shows me it will do a
> sequential scan.
> is this lack of a feature or i am wrong somewhere?
Is the query fast enough? How big is your table? What does explain
analyze select tell you?
Cheers,
mark
--
mark@mielke.cc / markm@ncf.ca / markm@nortel.com __________________________
. . _ ._ . . .__ . . ._. .__ . . . .__ | Neighbourhood Coder
|\/| |_| |_| |/ |_ |\/| | |_ | |/ |_ |
| | | | | \ | \ |__ . | | .|. |__ |__ | \ |__ | Ottawa, Ontario, Canada
One ring to rule them all, one ring to find them, one ring to bring them all
and in the darkness bind them...
http://mark.mielke.cc/
^ permalink raw reply [nested|flat] 9+ messages in thread
* Re: LIKE query on indexes
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 17:40 ` Re: LIKE query on indexes mark@mark.mielke.cc
@ 2006-02-21 20:12 ` Ibrahim Tekin <itekin@gmail.com>
0 siblings, 0 replies; 9+ messages in thread
From: Ibrahim Tekin @ 2006-02-21 20:12 UTC (permalink / raw)
To: mark@mark.mielke.cc <mark@mark.mielke.cc>; +Cc: pgsql-performance
my database encoding is unicode.
i have two table, one is 3.64gb on hdd and has 2.2 million records. it takes
140 secs to run on my AMD Turion 64 M 800MHz/1GB laptop.
second table is 1.2gb, 220000 records, and takes 56 secs to run.
explain says 'Seq Scan on mytable, ..'
On 2/21/06, mark@mark.mielke.cc <mark@mark.mielke.cc> wrote:
>
> On Tue, Feb 21, 2006 at 05:57:12PM +0200, Ibrahim Tekin wrote:
> > i have btree index on a text type field. i want see rows which starts
> with
> > certain characters on that field. so i write a query like this:
> > SELECT * FROM mytable WHERE myfield LIKE 'john%'
> > since this condition is from start of the field, query planner should
> use
> > index to find such elements but explain command shows me it will do a
> > sequential scan.
> > is this lack of a feature or i am wrong somewhere?
>
> Is the query fast enough? How big is your table? What does explain
> analyze select tell you?
>
> Cheers,
> mark
>
> --
> mark@mielke.cc / markm@ncf.ca / markm@nortel.com
> __________________________
> . . _ ._ . . .__ . . ._. .__ . . . .__ | Neighbourhood Coder
> |\/| |_| |_| |/ |_ |\/| | |_ | |/ |_ |
> | | | | | \ | \ |__ . | | .|. |__ |__ | \ |__ | Ottawa, Ontario,
> Canada
>
> One ring to rule them all, one ring to find them, one ring to bring them
> all
> and in the darkness bind them...
>
> http://mark.mielke.cc/
>
>
^ permalink raw reply [nested|flat] 9+ messages in thread
end of thread, other threads:[~2006-02-23 12:52 UTC | newest]
Thread overview: 9+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2006-02-21 15:57 LIKE query on indexes Ibrahim Tekin <itekin@gmail.com>
2006-02-21 16:18 ` Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 16:34 ` Alvaro Herrera <alvherre@commandprompt.com>
2006-02-21 16:42 ` Scott Marlowe <smarlowe@g2switchworks.com>
2006-02-21 20:28 ` Ibrahim Tekin <itekin@gmail.com>
2006-02-22 15:48 ` Brendan Duddridge <brendan@clickspace.com>
2006-02-23 12:52 ` Ibrahim Tekin <itekin@gmail.com>
2006-02-21 17:40 ` mark@mark.mielke.cc
2006-02-21 20:12 ` Ibrahim Tekin <itekin@gmail.com>
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox