Re: like/ilike improvements

mark@mark.mielke.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