Re: query planner: automatic rescribe of LIKE to BETWEEN ?

Thomas Samson wrote:
> On 8/22/06, Alvaro Herrera  wrote:
> >Ulrich Habel wrote:
> >> Hello all,
> >> had an idea of optimizing a query that may work generally.
> >>
> >> In case a 'column' is indexed, following two alterations could be done
> >> I think:
> >>
> >> A)
> >>
> >>   select ... where column ~ '^Foo'     -->  Seq Scan
> >
> >This is not true.  You can make this query use an index if you create it
> >with opclass varchar_pattern_ops or text_pattern_ops, as appropiate.
> >
> >Thus you don't need any hack here.
> >
> 
> And in the case of more general expression, like:
> select ... where column ~ 'something';
> 
> Is there a way to optimise this ? (in the case where 'something' is not
> a word, but a part of a word)

Not sure.  I'd try tsearch2 or pg_trgm (or pg_tgrm, whatever it's
called).  It's trigram indexing.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support