Re: How to boost performance of ilike queries ?

Actually the query is created like this.
User enters the query in a user interface. User can type any character
in the query criteria. ie. % and _ can be at any place. User have the
freedom to choose query columns as well. The query is agianst a single
table .

rgds
Antony Paul


On Tue, 25 Jan 2005 19:49:12 +1100, Russell Smith <mr-russ@pws.com.au> wrote:
> On Tue, 25 Jan 2005 07:23 pm, Antony Paul wrote:
> > Creating an index and using lower(column) does not change the explain
> > plan estimates.
> > It seems that it is not using index for like or ilike queries
> > irrespective of whether it have a pattern matching character in it or
> > not. (using PostgreSQL 7.3.3)
> >
> > On googling I found this thread
> >
> > http://archives.postgresql.org/pgsql-sql/2004-11/msg00285.php
> >
> > It says that index is not used if the search string begins with a % symbol.
>
> What exactly are the type of like queries you are going?  there is a solution
> for having the % at the start, but you can win everyway.
>
> >
> > rgds
> > Antony Paul
> >
> > On Mon, 24 Jan 2005 20:58:54 +1100, Russell Smith <mr-russ@pws.com.au> wrote:
> > > On Mon, 24 Jan 2005 08:18 pm, Antony Paul wrote:
> > > > Hi,
> > > >     I have a query which is executed using ilike. The query values are
> > > > received from user and it is executed using PreparedStatement.
> > > > Currently all queries are executed as it is using iilike irrespective
> > > > of whether it have a pattern matching character or not. Can using =
> > > > instead of ilike boot performance ?.  If creating index can help then
> > > > how the index should be created on lower case or uppercase ?.
> > > >
> > > It depends on the type of queries you are doing.
> > >
> > > changing it to something like  lower(column) like lower('text%'), and
> > > creating an index on lower(column) will give you much better performance.
> > >
> > > If you have % in the middle of the query, it will still be slow, but I assume that is not
> > > the general case.
> > >
> > > I am not sure what the effect of it being prepared will be, however I've had much success
> > > with the method above without the queries being prepared.  Others may be able to offer advice
> > > about if prepare will effect it.
> > >
> > > Regards
> > >
> > > Russell Smith
> > >
> >
> >
>