Re: String matching

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Re: String matching

От:
Stephan Szabo <sszabo@megazone.bigpanda.com>
Дата:
On Mon, 14 Feb 2005, Ivan Voras wrote:

> PFC wrote:
> >
> >     normally you shouldn't have to do anything, it should just work :
> >
> >> select field from table where field like 'abc%'
>
> >     If it does not use the index, I saw on the mailing list that the
> > locale  could be an issue.
>
> Oh yes, I forgot about that :( I do have LC_COLLATE (on latin2)...
>
> It's a shame PostgreSQL doesn't allow collation rules on specific fields
> - this field I'm using here will always be 7bit ASCII :(

You can also create an index using a _pattern_ops operator
class which should be usable even with other collations.

Re: String matching

От:
Stephan Szabo <sszabo@megazone.bigpanda.com>
Дата:

On Mon, 14 Feb 2005, Ivan Voras wrote:

> Stephan Szabo wrote:
>
> > You can also create an index using a _pattern_ops operator
> > class which should be usable even with other collations.
>
> Could you give me an example for this, or point me to the relevant
> documentation?

Basically, you could have something like:

create table test_table(a text);
create index test_index on test_table(a text_pattern_ops);

------------------------------------------------------------------

http://www.postgresql.org/docs/8.0/interactive/indexes-opclass.html

Re: String matching

От:
Stephan Szabo <sszabo@megazone.bigpanda.com>
Дата:
On Mon, 14 Feb 2005, Ivan Voras wrote:

> Stephan Szabo wrote:
> > On Mon, 14 Feb 2005, Ivan Voras wrote:
>
> >>Could you give me an example for this, or point me to the relevant
> >>documentation?
>
> >
> > http://www.postgresql.org/docs/8.0/interactive/indexes-opclass.html
>
> Thanks! I didn't know this and I certainly didn't think it would be that
> easy :)

Well, it's not perfect. It requires a separate index from one for normal
comparisons, so it's trading modification speed for LIKE lookup speed.

String matching

От:
Ivan Voras <ivoras@fer.hr>
Дата:
Is there a way to use indexes for queries like:

select field from table where field like 'abc%'

(i.e. filter for string fields that begin with something) ?

Re: String matching

От:
Ivan Voras <ivoras@fer.hr>
Дата:
PFC wrote:
> 
>     normally you shouldn't have to do anything, it should just work :
> 
>> select field from table where field like 'abc%'

>     If it does not use the index, I saw on the mailing list that the 
> locale  could be an issue.

Oh yes, I forgot about that :( I do have LC_COLLATE (on latin2)...

It's a shame PostgreSQL doesn't allow collation rules on specific fields 
- this field I'm using here will always be 7bit ASCII :(

Re: String matching

От:
Ivan Voras <ivoras@fer.hr>
Дата:
Stephan Szabo wrote:

> You can also create an index using a _pattern_ops operator
> class which should be usable even with other collations.

Could you give me an example for this, or point me to the relevant 
documentation?

Re: String matching

От:
Ivan Voras <ivoras@fer.hr>
Дата:
Stephan Szabo wrote:
> On Mon, 14 Feb 2005, Ivan Voras wrote:

>>Could you give me an example for this, or point me to the relevant
>>documentation?

> 
> http://www.postgresql.org/docs/8.0/interactive/indexes-opclass.html

Thanks! I didn't know this and I certainly didn't think it would be that
easy :)

Re: String matching

От:
PFC <lists@boutiquenumerique.com>
Дата:

	normally you shouldn't have to do anything, it should just work :

> select field from table where field like 'abc%'

CREATE INDEX ... ON table( field );

	that's all

	If it does not use the index, I saw on the mailing list that the locale  
could be an issue.
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