Re: Case Insensitive searches

I have read the article... tnks, very helpful.

But, can I create a index using function like "substring"? I would like to
create something like this:

CREATE INDEX indtest_01 ON table_01
((SUBSTRING(month_year, 3, 4) || SUBSTRING(month_year, 1, 2))

2008/8/4 Terry Lee Tucker <terry(at)chosen-ones(dot)org>

> On Monday 04 August 2008 11:09, Frank Bax wrote:
> > Terry Lee Tucker wrote:
> > > On Monday 04 August 2008 10:05, Richard Broersma wrote:
> > >> On Mon, Aug 4, 2008 at 6:54 AM, Mike Gould <mgould(at)allcoast(dot)net>
> wrote:
> > >>> In some db's if you
> > >>> use a lower() or upr() it will always do a table scan instead of
> using
> > >>> a index
> > >>
> > >> True, this would also happen in PostgreSQL. However, you can overcome
> > >> this by creating a "functional" index:
> > >>
> > >>
> http://www.postgresql.org/docs/8.3/interactive/indexes-expressional.html
> > >>
> > >> This way all expression using where lower( column ) = 'a'. will always
> > >> use an index scan.
> > >
> > > What about using the operator, ~* ?
> > >
> > > Does that cause a table scan as well?
> >
> > Whether or not any query uses an index scan or seq scan depends on many
> > factors and is not always easily predictable.
> >
> > Richard's statement about "will always use an index scan" is not
> > universally true. If the table is very small; a index scan is NOT used.
> > Table statistics could also indicate a seq scan is more efficient
> > (suppose 99% of rows had column='a').
> >
> > The ~* operator is very likely to scan the entire table because it will
> > look for 'A' anywhere in the column (and will therefore match 'Joanne';
> > and I doubt that there is special code to handle case where length of
> > argument is exactly the same as column. However; ~* '^a' which anchors
> > search to first character is perhaps more likely to use an index scan.
> >
> > Frank
>
> Frank,
>
> Thanks for the response. Actually, from within the applicaion, we use ~*
> and
> it is anchored with whatever they've typed in the widget as search
> criteria.
>
> Anyway, thanks for the helpful response...
> --
> Terry Lee Tucker
> Turbo's IT Manager
> Turbo, division of Ozburn-Hessey Logistics
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>
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