Subject: Re: [HACKERS] Efficient DELETE Strategies
From: Hannu Krosing <hannu@tm.ee>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Christoph Haller <ch@rodos.fzk.de>,
	pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
In-Reply-To: <200206110253.g5B2r0g14419@candle.pha.pa.us>
References: <200206110253.g5B2r0g14419@candle.pha.pa.us>
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Date: 11 Jun 2002 12:02:49 +0200
Message-Id: <1023789769.6942.44.camel@taru.tm.ee>
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On Tue, 2002-06-11 at 04:53, Bruce Momjian wrote:
> Tom Lane wrote:
> > Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > > Hannu Krosing wrote:
> > >> What about
> > >> 
> > >> DELETE relation_expr FROM relation_expr [ , table_ref [ , ... ] ]
> > >> [ WHERE bool_expr ]
> > >> 
> > >> or
> > >> 
> > >> DELETE relation_expr.* FROM relation_expr [ , table_ref [ , ... ] ]
> > >> [ WHERE bool_expr ]
> > 
> > > So make the initial FROM optional and allow the later FROM to be a list
> > > of relations?  Seems kind of strange.

I was inspired by MS Access syntax that has optional relation_expr.* :

   DELETE [relation_expr.*] FROM relation_expr WHERE criteria

it does not allow any other tablerefs in from 

> Clearly this is a TODO item.  I will document it when we decide on a
> direction.

Or then we can just stick with standard syntax and teach people to do

DELETE FROM t1 where t1.id1 in 
 (select id2 from t2 where t2.id2 = t1.id1)

and perhaps even teach our optimizer to add the t2.id2 = t1.id1 part
itself to make it fast

AFAIK this should be exactly the same as the proposed

DELETE FROM t1 FROM t2
WHERE t2.id2 = t1.id1

--------------
Hannu