To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Hannu Krosing <hannu@tm.ee>, Christoph Haller <ch@rodos.fzk.de>,
	pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Efficient DELETE Strategies 
In-reply-to: <200206101833.g5AIXj600263@candle.pha.pa.us> 
References: <200206101833.g5AIXj600263@candle.pha.pa.us>
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
	message dated "Mon, 10 Jun 2002 14:33:45 -0400"
Date: Mon, 10 Jun 2002 16:34:01 -0400
Message-ID: <8490.1023741241@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

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.

No, I think he's suggesting that one be able to pick out any element of
the FROM-list and say that that is the deletion target.  I really don't
want to get into that (unless there is precedent in Oracle or
someplace); it seems way too confusing to me.  It would also force us to
do error checking to eliminate cases that ought to just be syntactically
impossible: target table not present, target is a join or subselect
instead of a table, target is on wrong side of an outer join, etc.

[ and in another message ]
> The FROM ... FROM looks weird, and there is clearly confusion over the
> FROM t1, t2.  I wish there was another option.

The only other thing that's come to mind is to use a different keyword
(ie, not FROM) for the list of auxiliary relations.  WITH might work
from a simple readability point of view:
	DELETE FROM target WITH other-tables WHERE ...
But we've already got FROM as the equivalent construct in UPDATE, so it
seems weird to use something else in DELETE.

			regards, tom lane