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Re: Implementation of LIMIT on DELETE and UPDATE statements

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Alvaro Herrera <alvherre(at)atentus(dot)com>,"Stephen R(dot) van den Berg" <srb(at)cuci(dot)nl>, pgsql-patches(at)postgresql(dot)org
Subject: Re: Implementation of LIMIT on DELETE and UPDATE statements
Date: 2002-09-23 03:12:43
Message-ID: 200209230312.g8N3ChC05510@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Tom Lane wrote:
> > srb(at)cuci(dot)nl (Stephen R. van den Berg) escribi:
> >> Incidentally, using a SELECT without an ORDER BY but with a LIMIT is
> >> documented to give unpredictable results, yet users are expected cope with
> >> this fact, but are expected to have problems with a similar fact in
> >> an UPDATE or DELETE statement?
> 
> Well, IMHO there's a big difference in documented unpredictable output
> from a documented-unpredictable query, as opposed to
> documented-unpredictable changes in the database state.  There is not
> a lot of use for the latter AFAICS.
> 
> Alvaro Herrera <alvherre(at)atentus(dot)com> writes:
> > as I already said, the feature has some value with the ORDER BY added,
> > and the LIMIT/OFFSET thing expanded to allow expressions (this last part
> > is in TODO).
> 
> I'd have more confidence in the usefulness of the idea if it included
> ORDER BY to make the LIMIT predictable.  But before you run off and
> implement that: does MySQL support such a thing?  If not, the argument
> of improving compatibility still doesn't hold any water...

I see no reason to add stuff to UPDATE/DELETE when a subquery does the
job just as well.  It just seems like bloat.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

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Subject: HISTORY updated for 7.3beta2
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Subject: Re: Implementation of LIMIT on DELETE and UPDATE statements (rel to 7.2.1)

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