Re: [GENERAL] Long update query ? - Mailing list pgsql-general

From Bruce Momjian
Subject Re: [GENERAL] Long update query ?
Date
Msg-id 199810012254.SAA18974@candle.pha.pa.us
Whole thread Raw
In response to RE: [GENERAL] Long update query ?  ("Taral" <taral@mail.utexas.edu>)
Responses Re: [GENERAL] Long update query ? (also Re: [GENERAL] CNF vs. DNF)
List pgsql-general
[Charset iso-8859-1 unsupported, filtering to ASCII...]
> > This is caused by a semi-well known weakness in the optimizer.
> > The optimizer
> > rewrites the WHERE clause in conjunctive normal form (CNF):
> >
> >    (A and B) or (C and D) ==>  (A or C) and (A or D) and (B or C)
> > and (B or D)
> >
>
> Wouldn't disjunctive normal form be better, since it can be implemented as
> the simple union of a set of small queries?

Please tell us more.

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