Re: NOT LIKE much faster than LIKE?

On Wed, Jan 11, 2006 at 12:40:32PM -0600, Jim C. Nasby wrote:
> On Tue, Jan 10, 2006 at 02:44:47AM +0100, Andrea Arcangeli wrote:
> > "cooperative" runs "WHERE kernel_version NOT LIKE '%% PREEMPT %%'", while
> > "preempt" runs "WHERE kernel_version LIKE '%% PREEMPT %%'. The only difference
>
> One thing you could do is change the like to:
>
> WHERE position(' PREEMPT ' in kernel_version) != 0

That alone fixed it, with this I don't even need the index (yet). Thanks
a lot.

> And then create a functional index on that:
>
> CREATE INDEX indexname ON tablename ( position(' PREEMPT ' in kernel_version) );

The index only helps the above query with = 0 and not the one with != 0,
but it seems not needed in practice.