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Re: [GENERAL] Long update query ? (also Re: [GENERAL] CNF vs. DNF)

From: "Taral" <taral(at)mail(dot)utexas(dot)edu>
To: "Bruce Momjian" <maillist(at)candle(dot)pha(dot)pa(dot)us>
Cc: <pgsql-general(at)postgreSQL(dot)org>
Subject: Re: [GENERAL] Long update query ? (also Re: [GENERAL] CNF vs. DNF)
Date: 1998-10-01 23:45:33
Message-ID: 000001bded95$94a20cc0$3b291f0a@taral (view raw, whole thread or download thread mbox)
Lists: pgsql-generalpgsql-hackers
> > 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.

Well, I don't know how the backend processes queries, but one can imagine
this scenario (for DNF):

1) Analyze query and set up columns in result table
2) Rewrite query into DNF
3) Split query into subqueries
4) For each subquery:
  a) Process query
  b) Append matching tuples to result table
5) Do any post-processing (ORDER BY, etc.)
6) Return result

How is the processing currently done (with CNF)?


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