Re: like/ilike improvements

mark(at)mark(dot)mielke(dot)cc wrote:
>
>
> Is it worth the effort to pre-process the pattern?
>
> For example:
>
> %% -> %
>

This is already done, required by spec.

> %_ -> _%
>
> If applied recursively, this would automatically cover:
>
> %_% -> _%
> _%_ -> __%
>
> The 'benefit' would be that the pattern matching code would not
> need an inner if statement?
>

I doubt it's worth the trouble.

> Also - I didn't see a response to my query with regard treating UTF-8
> as a two pass match. First pass treating it as bytes. If the first pass
> matches, the second pass doing a full analysis. In the case of low
> selectivity, this will be a win, as the primary filter would be the
> full speed byte-based matching.
>

All matching will now be done byte-wise. CHAREQ is dead.

Advancing will also be done byte-wise except for:
. where text matching is against _ for UTF8
. where text matching is against % or _ for other multi-byte charsets.

So two passes doesn't sound like much of a win.
> I had also asked why the focus would be on high selectivity. Why would
> the primary filter criteria for a properly designed select statement by
> a like with high selectivity? The only time I have ever used like is
> when I expect low selectivity. Is there a reasonable case I am missing?
>
>
>

I think you'd need to show something close to a Pareto improvement:
nobody worse off and some people better off. If you can do that then
send in a patch.

However, I'm trying to minimise special case processing for UTF8, not
create a whole new code path for it. The less special cases we have the
easier it will be to maintain.

cheers

andrew