From: | Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | vadim(at)sable(dot)krasnoyarsk(dot)su (Vadim B(dot) Mikheev) |
Cc: | hackers(at)postgreSQL(dot)org |
Subject: | Re: [PATCHES] Re: [HACKERS] Query->hasSubLinks is always FALSE... |
Date: | 1998-02-09 17:33:59 |
Message-ID: | 199802091733.MAA14949@candle.pha.pa.us |
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Lists: | pgsql-hackers |
>
> Bruce Momjian wrote:
> >
> > You know, after all our lengthy discussions, this SubLink thing looks
> > pretty clean to me.
> >
> > How are subselects going? Are you having to write a lot of code to get
> > it working? I would say after all our discussions and thinking, it took
>
> Mmm ... =~ 1000 lines of code :)
>
> > me about two or three days to do the parser and rewrite for sublinks.
> > How many coding days is the rest taking? I am curious.
>
> All was near ready Feb 6, but ... I got problems from canonification
> routines in optimizer: 'where A AND B OR C ' becomes 'where (A OR C) AND (B OR C)'
> and if C is subselect then ... C has to be processed twice (sometime) ...
> I remember your question about handling 'A AND (B OR SubSelect)' - unfortunately,
> I didn't see problems here (actually, there is no problem with this
> conjunctive normal form :), but there are troubles in common case.
>
> Ideas ?
>
> For the moment I could leave this un-optimized, with possibility
> of double subselect processing...
I would leave it for later. We already have an optimizer explosion
problem when we have lots of OR's so at some point we may have to
revisit the cnf-ify process anyway. Commerical Ingres has or had the
same problem.
--
Bruce Momjian
maillist(at)candle(dot)pha(dot)pa(dot)us
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