I have applied the following patch to clarify the current behavior.
Thanks.
---------------------------------------------------------------------------
Jim C. Nasby wrote:
> On Tue, Jan 17, 2006 at 03:44:30PM +0100, Magnus Hagander wrote:
> > > > http://www.postgresql.org/docs/8.1/static/indexes-types.html
> > > > says:
> > > > The optimizer can also use a B-tree index for queries involving the
> > > > pattern matching operators LIKE, ILIKE, ~, and ~*, if the
> > > pattern is a
> > > > constant and is anchored to the beginning of the string -
> > > for example,
> > > > col LIKE 'foo%' or col ~ '^foo', but not col LIKE '%bar'.
> > >
> > > > But really, does it use indexes for ILIKE?
> > >
> > > That's pretty poorly phrased. For ILIKE it'll only work if
> > > there's a prefix of the pattern that's not letters (and hence
> > > is unaffected by the case-folding issue).
> >
> > Ahh. That explains it. Perfectly logical.
> > And yes, that's pretty poorly phrased - at least I didn't understand it
> > :-)
>
> I was going to submit a patch on this, and the best way seems to be
> adding a note to 'ILIKE', specifying that it will only work if there's a
> prefix to the pattern that isn't letters. Is there a standard way to tag
> a word indicating that there's a note?
> --
> Jim C. Nasby, Sr. Engineering Consultant [EMAIL PROTECTED]
> Pervasive Software http://pervasive.com work: 512-231-6117
> vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
>
> ---------------------------(end of broadcast)---------------------------
> TIP 9: In versions below 8.0, the planner will ignore your desire to
> choose an index scan if your joining column's datatypes do not
> match
>
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
Index: doc/src/sgml/indices.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/indices.sgml,v
retrieving revision 1.55
diff -c -c -r1.55 indices.sgml
*** doc/src/sgml/indices.sgml 7 Nov 2005 17:36:44 -0000 1.55
--- doc/src/sgml/indices.sgml 18 Jan 2006 21:24:06 -0000
***************
*** 141,157 ****
<para>
The optimizer can also use a B-tree index for queries involving the
! pattern matching operators <literal>LIKE</>,
! <literal>ILIKE</literal>, <literal>~</literal>, and
! <literal>~*</literal>, <emphasis>if</emphasis> the pattern is a constant
! and is anchored to the beginning of the string — for example,
! <literal>col LIKE 'foo%'</literal> or <literal>col ~ '^foo'</literal>,
! but not <literal>col LIKE '%bar'</literal>. However, if your server does
! not use the C locale you will need to create the index with a
! special operator class to support indexing of pattern-matching queries.
! See <xref linkend="indexes-opclass"> below.
</para>
<para>
<indexterm>
<primary>index</primary>
--- 141,161 ----
<para>
The optimizer can also use a B-tree index for queries involving the
! pattern matching operators <literal>LIKE</> and <literal>~</literal>
! <emphasis>if</emphasis> the pattern is a constant and is anchored to
! the beginning of the string — for example, <literal>col LIKE
! 'foo%'</literal> or <literal>col ~ '^foo'</literal>, but not
! <literal>col LIKE '%bar'</literal>. However, if your server does not
! use the C locale you will need to create the index with a special
! operator class to support indexing of pattern-matching queries. See
! <xref linkend="indexes-opclass"> below. It is also possible to use
! B-tree indexes for <literal>ILIKE</literal> and
! <literal>~*</literal>, but only if the pattern starts with
! non-alphabetic characters, i.e. characters that are not affected by
! upper/lower case conversion.
</para>
+
<para>
<indexterm>
<primary>index</primary>
---------------------------(end of broadcast)---------------------------
TIP 6: explain analyze is your friend
