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From pgsql-sql-owner+M8069=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 07:42:52 2002
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From: Christoph Haller <ch@rodos.fzk.de>
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Message-ID: <200206101142.NAA16854@rodos>
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Subject: [SQL] Efficient DELETE Strategies
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To: pgsql-sql@postgresql.org
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Date: Mon, 10 Jun 2002 13:42:10 METDST
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X-Mailer: Elm [revision: 212.4]
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Precedence: bulk
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Sender: pgsql-sql-owner@postgresql.org
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Status: OR
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Hi,
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Based on an entry in the mailing list from 30 Oct 2001
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about efficient deletes on subqueries,
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I've found two ways to do so (PostgreSQL 7.2.1):
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1.
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BEGIN ;
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EXPLAIN ANALYZE
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DELETE FROM onfvalue WHERE EXISTS(
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SELECT * FROM onfvalue j WHERE
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j.sid= 5 AND
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onfvalue.lid = j.lid AND
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onfvalue.mid = j.mid AND
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onfvalue.timepoint = j.timepoint AND
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onfvalue.entrancetime < j.entrancetime
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) ;
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ROLLBACK ;
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QUERY PLAN:
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Seq Scan on onfvalue
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(cost=0.00..805528.05 rows=66669 width=6)
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(actual time=61.84..25361.82 rows=24 loops=1)
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SubPlan
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-> Index Scan using advncd_onfvalue_idx_stlme on onfvalue j
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(cost=0.00..6.02 rows=1 width=36)
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(actual time=0.14..0.14 rows=0 loops=133338)
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Total runtime: 25364.76 msec
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2.
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BEGIN ;
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EXPLAIN ANALYZE
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INSERT INTO temprefentrancetime(timepoint,lid,mid,sid,entrancetime)
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SELECT o.timepoint,o.lid,o.mid,o.sid,o.entrancetime
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FROM onfvalue o join onfvalue j ON (
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o.lid = j.lid AND
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o.mid = j.mid AND
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o.timepoint = j.timepoint AND
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o.entrancetime < j.entrancetime
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) WHERE o.sid= 5 ;
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EXPLAIN ANALYZE
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DELETE FROM onfvalue WHERE
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onfvalue.timepoint = temprefentrancetime.timepoint AND
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onfvalue.mid = temprefentrancetime.mid AND
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onfvalue.lid = temprefentrancetime.lid AND
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onfvalue.sid = temprefentrancetime.sid AND
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onfvalue.entrancetime = temprefentrancetime.entrancetime ;
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DELETE FROM temprefentrancetime;
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ROLLBACK ;
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QUERY PLAN:
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Merge Join
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(cost=16083.12..16418.36 rows=4 width=52)
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(actual time=17728.06..19325.02 rows=24 loops=1)
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-> Sort
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(cost=2152.53..2152.53 rows=667 width=28)
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(actual time=1937.70..2066.46 rows=16850 loops=1)
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-> Index Scan using advncd_onfvalue_idx_stlme on onfvalue o
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(cost=0.00..2121.26 rows=667 width=28)
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(actual time=0.57..709.89 rows=16850 loops=1)
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-> Sort
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(cost=13930.60..13930.60 rows=133338 width=24)
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(actual time=13986.07..14997.43 rows=133110 loops=1)
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-> Seq Scan on onfvalue j
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(cost=0.00..2580.38 rows=133338 width=24)
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(actual time=0.15..3301.06 rows=133338 loops=1)
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Total runtime: 19487.49 msec
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QUERY PLAN:
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Nested Loop
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(cost=0.00..6064.40 rows=1 width=62)
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(actual time=1.34..8.32 rows=24 loops=1)
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-> Seq Scan on temprefentrancetime
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(cost=0.00..20.00 rows=1000 width=28)
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(actual time=0.44..1.07 rows=24 loops=1)
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-> Index Scan using advncd_onfvalue_idx_stlme on onfvalue
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(cost=0.00..6.02 rows=1 width=34)
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(actual time=0.22..0.25 rows=1 loops=24)
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Total runtime: 10.15 msec
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The questions are:
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Is there a way to put the second form (more complicated, but faster)
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in one statement?
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Or is there even a third way to delete, which I cannot see?
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Regards, Christoph
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From pgsql-sql-owner+M8075=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 12:03:46 2002
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id EBA4C475B88; Mon, 10 Jun 2002 09:56:50 -0400 (EDT)
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Mon, 10 Jun 2002 09:56:28 -0400 (EDT)
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To: Christoph Haller <ch@rodos.fzk.de>
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cc: pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
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Subject: Re: [SQL] Efficient DELETE Strategies
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In-Reply-To: <200206101142.NAA16854@rodos>
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References: <200206101142.NAA16854@rodos>
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Comments: In-reply-to Christoph Haller <ch@rodos.fzk.de>
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message dated "Mon, 10 Jun 2002 13:42:10 +0700"
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Date: Mon, 10 Jun 2002 09:56:27 -0400
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Message-ID: <5619.1023717387@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Precedence: bulk
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Sender: pgsql-sql-owner@postgresql.org
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Status: ORr
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Christoph Haller <ch@rodos.fzk.de> writes:
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> Based on an entry in the mailing list from 30 Oct 2001
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> about efficient deletes on subqueries,
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> I've found two ways to do so (PostgreSQL 7.2.1):
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> ...
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> Is there a way to put the second form (more complicated, but faster)
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> in one statement?
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> Or is there even a third way to delete, which I cannot see?
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The clean way to do this would be to allow extra FROM-list relations
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in DELETE. We already have a similar facility for UPDATE, so it's not
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clear to me why there's not one for DELETE. Then you could do, say,
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DELETE FROM onfvalue , onfvalue j WHERE
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j.sid= 5 AND
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onfvalue.lid = j.lid AND
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onfvalue.mid = j.mid AND
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onfvalue.timepoint = j.timepoint AND
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onfvalue.entrancetime < j.entrancetime ;
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If you were using two separate tables you could force this to happen
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via an implicit FROM-clause entry, much as you've done in your second
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alternative --- but there's no way to set up a self-join in a DELETE
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because of the lack of any place to put an alias declaration.
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AFAIK this extension would be utterly trivial to implement, since all
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the machinery is there already --- for 99% of the backend, it doesn't
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matter whether a FROM-item is implicit or explicit. We'd only need to
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argue out what the syntax should be. I could imagine
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DELETE FROM relation_expr [ , table_ref [ , ... ] ]
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[ WHERE bool_expr ]
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or
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DELETE FROM relation_expr [ FROM table_ref [ , ... ] ]
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[ WHERE bool_expr ]
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The two FROMs in the second form look a little weird, but they help to
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make a clear separation between the deletion target table and the
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merely-referenced tables. Also, the first one might look to people
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like they'd be allowed to write
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DELETE FROM foo FULL JOIN bar ...
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which is not any part of my intention (it's very unclear what it'd
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mean for the target table to be on the nullable side of an outer join).
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OTOH there'd be no harm in outer joins in a separate from-clause, eg
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DELETE FROM foo FROM (bar FULL JOIN baz ON ...) WHERE ...
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Actually, either syntax above would support that; I guess what's really
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bothering me about the first syntax is that a comma suggests a list of
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things that will all be treated similarly, while in reality the first
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item will be treated much differently from the rest.
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Does anyone know whether other systems that support the UPDATE extension
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for multiple tables also support a DELETE extension for multiple tables?
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If so, what's their syntax?
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A somewhat-related issue is that people keep expecting to be able to
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attach an alias to the target table name in UPDATE and DELETE; seems
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like we get that question every couple months. While this is clearly
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disallowed by the SQL spec, it's apparently supported by some other
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implementations (else we'd not get the question so much). Should we
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add that extension to our syntax? Or should we continue to resist it?
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regards, tom lane
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From pgsql-sql-owner+M8084=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 17:29:55 2002
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From: Manfred Koizar <mkoi-pg@aon.at>
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To: Tom Lane <tgl@sss.pgh.pa.us>
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cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org,
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pgsql-hackers@postgresql.org
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Subject: Re: [SQL] Efficient DELETE Strategies
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Date: Mon, 10 Jun 2002 22:23:38 +0200
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Message-ID: <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com>
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References: <200206101142.NAA16854@rodos> <5619.1023717387@sss.pgh.pa.us>
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In-Reply-To: <5619.1023717387@sss.pgh.pa.us>
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Status: OR
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On Mon, 10 Jun 2002 09:56:27 -0400, Tom Lane <tgl@sss.pgh.pa.us>
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wrote:
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>Does anyone know whether other systems that support the UPDATE extension
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>for multiple tables also support a DELETE extension for multiple tables?
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>If so, what's their syntax?
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MSSQL seems to guess what the user wants. All the following
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statements do the same:
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(0) DELETE FROM t1 WHERE EXISTS (SELECT * FROM t2 WHERE t1.i=t2.i)
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(1) DELETE t1 FROM t2 WHERE t1.i=t2.i
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(2a) DELETE t1 FROM t2, t1 WHERE t1.i=t2.i
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(2b) DELETE t1 FROM t2 INNER JOIN t1 ON t1.i=t2.i
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(3a) DELETE t1 FROM t2, t1 a WHERE a.i=t2.i
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(3b) DELETE t1 FROM t2 INNER JOIN t1 a ON a.i=t2.i
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(4a) DELETE a FROM t2, t1 a WHERE a.i=t2.i
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(4b) DELETE a FROM t2 INNER JOIN t1 a ON a.i=t2.i
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(5) DELETE t1 FROM t1 a
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WHERE EXISTS (SELECT * FROM t2 WHERE a.i=t2.i)
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(6) DELETE a FROM t1 a WHERE EXISTS (SELECT * FROM t2 WHERE a.i=t2.i)
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(0) is standard SQL and should always work. As an extension I'd like
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(1) or (2), but only one of them and forbid the other one. I'd also
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forbid (3), don't know what to think of (4), and don't see a reason
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why we would want (5) or (6). I'd rather have (7) or (8).
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These don't work:
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(7) DELETE t1 a FROM t2 WHERE a.i = t2.i
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"Incorrect syntax near 'a'."
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(8) DELETE FROM t1 a WHERE EXISTS (SELECT * FROM t2 WHERE a.i = t2.i)
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"Incorrect syntax near 'a'."
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Self joins:
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(2as) DELETE t1 FROM t1, t1 b WHERE 2*b.i=t1.i
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(4as) DELETE a FROM t1 a, t1 b WHERE 2*b.i=a.i
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(4bs) DELETE a FROM t1 a INNER JOIN t1 b on 2*b.i=a.i
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These don't work:
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DELETE t1 FROM t1 b WHERE 2 * b.i = t1.i
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"The column prefix 't1' does not match with a table name or alias name
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used in the query."
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DELETE t1 FROM t1 a, t1 b WHERE 2 * b.i = a.i
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"The table 't1' is ambiguous."
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And as if there aren't enough ways yet, I just discovered that (1) to
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(6) just as much work with "DELETE FROM" where I wrote "DELETE" ...
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Servus
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Manfred
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From pgsql-sql-owner+M8087=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 18:21:01 2002
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Mon, 10 Jun 2002 17:07:56 -0400 (EDT)
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To: Manfred Koizar <mkoi-pg@aon.at>
|
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cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org,
|
|
pgsql-hackers@postgresql.org
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Subject: Re: [SQL] Efficient DELETE Strategies
|
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In-Reply-To: <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com>
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References: <200206101142.NAA16854@rodos> <5619.1023717387@sss.pgh.pa.us> <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com>
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Comments: In-reply-to Manfred Koizar <mkoi-pg@aon.at>
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message dated "Mon, 10 Jun 2002 22:23:38 +0200"
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Date: Mon, 10 Jun 2002 17:07:56 -0400
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Message-ID: <8806.1023743276@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Precedence: bulk
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Sender: pgsql-sql-owner@postgresql.org
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Status: OR
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Manfred Koizar <mkoi-pg@aon.at> writes:
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>> If so, what's their syntax?
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> MSSQL seems to guess what the user wants.
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Gack. Nothing like treating mindless syntax variations as a "feature"
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list...
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> All the following statements do the same:
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> (1) DELETE t1 FROM t2 WHERE t1.i=t2.i
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> (2a) DELETE t1 FROM t2, t1 WHERE t1.i=t2.i
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> (5) DELETE t1 FROM t1 a
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> WHERE EXISTS (SELECT * FROM t2 WHERE a.i=t2.i)
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> (6) DELETE a FROM t1 a WHERE EXISTS (SELECT * FROM t2 WHERE a.i=t2.i)
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So in other words, MSSQL has no idea whether the name following DELETE
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is a real table name or an alias, and it's also unclear whether the name
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appears in the separate FROM clause or generates a FROM-item all by
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itself. This is why they have to punt on these cases:
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> These don't work:
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> DELETE t1 FROM t1 b WHERE 2 * b.i = t1.i
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> "The column prefix 't1' does not match with a table name or alias name
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> used in the query."
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> DELETE t1 FROM t1 a, t1 b WHERE 2 * b.i = a.i
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> "The table 't1' is ambiguous."
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The ambiguity is entirely self-inflicted...
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> And as if there aren't enough ways yet, I just discovered that (1) to
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> (6) just as much work with "DELETE FROM" where I wrote "DELETE" ...
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Hm. So (1) with the DELETE FROM corresponds exactly to what I was
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suggesting:
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DELETE FROM t1 FROM t2 WHERE t1.i=t2.i
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except that I'd also allow an alias in there:
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DELETE FROM t1 a FROM t2 b WHERE a.i=b.i
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Given the plethora of mutually incompatible interpretations that MSSQL
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evidently supports, though, I fear we can't use it as precedent for
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making any choices :-(.
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Can anyone check out other systems?
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regards, tom lane
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From pgsql-sql-owner+M8093=candle.pha.pa.us=pgman@postgresql.org Tue Jun 11 05:19:14 2002
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Return-path: <pgsql-sql-owner+M8093=candle.pha.pa.us=pgman@postgresql.org>
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Received: by rodos.fzk.de with ESMTP (8.8.6 (PHNE_17135)/8.7.1) id LAA02189 for <pgsql-sql@postgresql.org>; Tue, 11 Jun 2002 11:19:15 +0200 (METDST)
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From: Christoph Haller <ch@rodos.fzk.de>
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Message-ID: <200206110918.LAA20463@rodos>
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Subject: Re: [SQL] Efficient DELETE Strategies
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To: pgsql-sql@postgresql.org
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Date: Tue, 11 Jun 2002 11:18:34 METDST
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X-Mailer: Elm [revision: 212.4]
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Precedence: bulk
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Sender: pgsql-sql-owner@postgresql.org
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Status: OR
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Bruce Momjian wrote:
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> ...
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> Yes, another keyword is the only solution. Having FROM after DELETE
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> mean something different from FROM after a tablename is just too weird.
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> I know UPDATE uses FROM, and it is logical to use it here, but it is
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> just too wierd when DELETE already has a FROM. Should we allow FROM and
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> add WITH to UPDATE as well, and document WITH but support FROM too? No
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> idea. What if we support ADD FROM as the keywords for the new clause?
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Sounds like the best solution so far.
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Christopher Kings-Lynne wrote:
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> DELETE [LOW_PRIORITY | QUICK] table_name[.*] [,table_name[.*] ...]
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> FROM table-references
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> [WHERE where_definition]
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>
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> or
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>
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> DELETE [LOW_PRIORITY | QUICK]
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> FROM table_name[.*], [table_name[.*] ...]
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> USING table-references
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> [WHERE where_definition]
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>
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> ...
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> The idea is that only matching rows from the tables listed before the FROM
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> or before the USING clause are deleted. The effect is that you can delete
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> rows from many tables at the same time and also have additional tables that
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> are used for searching.
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Sounds tempting. It is much more what I was asking for.
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Is there a collision with USING ( join_column_list ) ?
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And it looks like very much work for the HACKERS.
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Hannu Krosing wrote:
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> ...
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> Or then we can just stick with standard syntax and teach people to do
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>
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> DELETE FROM t1 where t1.id1 in
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> (select id2 from t2 where t2.id2 = t1.id1)
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>
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> and perhaps even teach our optimizer to add the t2.id2 = t1.id1 part
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> itself to make it fast
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>
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> AFAIK this should be exactly the same as the proposed
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>
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> DELETE FROM t1 FROM t2
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> WHERE t2.id2 = t1.id1
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This is a fine idea. But it looks like very much work for the HACKERS, too.
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Regards, Christoph
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From pgsql-sql-owner+M8094=candle.pha.pa.us=pgman@postgresql.org Tue Jun 11 10:29:20 2002
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Return-path: <pgsql-sql-owner+M8094=candle.pha.pa.us=pgman@postgresql.org>
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Tue, 11 Jun 2002 10:28:41 -0400 (EDT)
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To: Christoph Haller <ch@rodos.fzk.de>
|
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cc: pgsql-sql@postgresql.org
|
|
Subject: Re: [SQL] Efficient DELETE Strategies
|
|
In-Reply-To: <200206110918.LAA20463@rodos>
|
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References: <200206110918.LAA20463@rodos>
|
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Comments: In-reply-to Christoph Haller <ch@rodos.fzk.de>
|
|
message dated "Tue, 11 Jun 2002 11:18:34 +0700"
|
|
Date: Tue, 11 Jun 2002 10:28:40 -0400
|
|
Message-ID: <18946.1023805720@sss.pgh.pa.us>
|
|
From: Tom Lane <tgl@sss.pgh.pa.us>
|
|
Precedence: bulk
|
|
Sender: pgsql-sql-owner@postgresql.org
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Status: OR
|
|
|
|
Christoph Haller <ch@rodos.fzk.de> writes:
|
|
> Christopher Kings-Lynne wrote:
|
|
>> DELETE [LOW_PRIORITY | QUICK] table_name[.*] [,table_name[.*] ...]
|
|
>> FROM table-references
|
|
>> [WHERE where_definition]
|
|
>>
|
|
>> or
|
|
>>
|
|
>> DELETE [LOW_PRIORITY | QUICK]
|
|
>> FROM table_name[.*], [table_name[.*] ...]
|
|
>> USING table-references
|
|
>> [WHERE where_definition]
|
|
>>
|
|
>> The idea is that only matching rows from the tables listed before the FROM
|
|
>> or before the USING clause are deleted. The effect is that you can delete
|
|
>> rows from many tables at the same time and also have additional tables that
|
|
>> are used for searching.
|
|
|
|
> Sounds tempting. It is much more what I was asking for.
|
|
> Is there a collision with USING ( join_column_list ) ?
|
|
|
|
Good point --- that was a very poor choice of keyword by the MySQL guys.
|
|
|
|
I have absolutely no intention of getting into this "delete from
|
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multiple tables" business --- I don't understand the semantics it should
|
|
have, and it would probably not be easy to do inside Postgres anyway.
|
|
|
|
It would seem that
|
|
|
|
DELETE [ FROM ] relation_expr [ alias_clause ]
|
|
[ FROM from_list ] where_clause
|
|
|
|
is the syntax that would be most nearly compatible with MSSQL and MySQL.
|
|
Does Oracle have anything comparable?
|
|
|
|
regards, tom lane
|
|
|
|
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From pgsql-sql-owner+M8112=candle.pha.pa.us=pgman@postgresql.org Wed Jun 12 10:04:47 2002
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for <tgl@sss.pgh.pa.us>; 12 Jun 2002 14:04:17 -0000
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From: Manfred Koizar <mkoi-pg@aon.at>
|
|
To: Tom Lane <tgl@sss.pgh.pa.us>
|
|
cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org
|
|
Subject: Re: [SQL] Efficient DELETE Strategies
|
|
Date: Wed, 12 Jun 2002 16:03:39 +0200
|
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Message-ID: <es9eguk7ov9644qo4qd341ess8ip8o51ok@4ax.com>
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References: <200206110918.LAA20463@rodos> <18946.1023805720@sss.pgh.pa.us>
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Status: ORr
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|
On Tue, 11 Jun 2002 10:28:40 -0400, Tom Lane <tgl@sss.pgh.pa.us>
|
|
wrote:
|
|
>It would seem that
|
|
>
|
|
> DELETE [ FROM ] relation_expr [ alias_clause ]
|
|
> [ FROM from_list ] where_clause
|
|
>
|
|
>is the syntax that would be most nearly compatible with MSSQL and MySQL.
|
|
>Does Oracle have anything comparable?
|
|
|
|
Oracle basically supports (with slight variations between releases
|
|
7/8/9):
|
|
DELETE [FROM] { table
|
|
| view
|
|
| ( subquery )
|
|
}
|
|
[alias] [WHERE ...] [returning_clause]
|
|
|
|
Informix (March 1997, 9.1?):
|
|
DELETE FROM { table
|
|
| ONLY ( table )
|
|
| view
|
|
| synonym
|
|
| collection_derived_table
|
|
}
|
|
WHERE condition
|
|
|
|
According to the "SQL Quick Syntax Guide" the WHERE clause is not
|
|
optional. Does anybody know, if this is a documentation bug?
|
|
"Guide to SQL, Syntax" (Feb 1998, v7.3, v8.2) says, the WHERE clause
|
|
is optional, as we'd expect.
|
|
|
|
Servus
|
|
Manfred
|
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From pgsql-sql-owner+M8113=candle.pha.pa.us=pgman@postgresql.org Wed Jun 12 10:53:12 2002
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Wed, 12 Jun 2002 10:49:26 -0400 (EDT)
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To: Manfred Koizar <mkoi-pg@aon.at>
|
|
cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org
|
|
Subject: Re: [SQL] Efficient DELETE Strategies
|
|
In-Reply-To: <es9eguk7ov9644qo4qd341ess8ip8o51ok@4ax.com>
|
|
References: <200206110918.LAA20463@rodos> <18946.1023805720@sss.pgh.pa.us> <es9eguk7ov9644qo4qd341ess8ip8o51ok@4ax.com>
|
|
Comments: In-reply-to Manfred Koizar <mkoi-pg@aon.at>
|
|
message dated "Wed, 12 Jun 2002 16:03:39 +0200"
|
|
Date: Wed, 12 Jun 2002 10:49:26 -0400
|
|
Message-ID: <9663.1023893366@sss.pgh.pa.us>
|
|
From: Tom Lane <tgl@sss.pgh.pa.us>
|
|
Precedence: bulk
|
|
Sender: pgsql-sql-owner@postgresql.org
|
|
Status: OR
|
|
|
|
Manfred Koizar <mkoi-pg@aon.at> writes:
|
|
> Oracle basically supports (with slight variations between releases
|
|
> 7/8/9):
|
|
> DELETE [FROM] { table
|
|
> | view
|
|
> | ( subquery )
|
|
> }
|
|
> [alias] [WHERE ...] [returning_clause]
|
|
|
|
Bizarre. How are you supposed to delete from a subquery?
|
|
|
|
> According to the "SQL Quick Syntax Guide" the WHERE clause is not
|
|
> optional. Does anybody know, if this is a documentation bug?
|
|
|
|
Probably. SQL92 saith:
|
|
|
|
<delete statement: searched> ::=
|
|
DELETE FROM <table name>
|
|
[ WHERE <search condition> ]
|
|
|
|
<delete statement: positioned> ::=
|
|
DELETE FROM <table name>
|
|
WHERE CURRENT OF <cursor name>
|
|
|
|
so I could see where a sloppy reader might get confused...
|
|
|
|
regards, tom lane
|
|
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|
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From pgsql-sql-owner+M8118=candle.pha.pa.us=pgman@postgresql.org Wed Jun 12 14:26:01 2002
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From: Manfred Koizar <mkoi-pg@aon.at>
|
|
To: Tom Lane <tgl@sss.pgh.pa.us>
|
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cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org
|
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Subject: Re: [SQL] Efficient DELETE Strategies
|
|
Date: Wed, 12 Jun 2002 20:06:11 +0200
|
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Message-ID: <dgqeguc0kf8ord0g37vo3hm6maqk649jak@4ax.com>
|
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References: <200206110918.LAA20463@rodos> <18946.1023805720@sss.pgh.pa.us> <es9eguk7ov9644qo4qd341ess8ip8o51ok@4ax.com> <9663.1023893366@sss.pgh.pa.us>
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Status: OR
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On Wed, 12 Jun 2002 10:49:26 -0400, Tom Lane <tgl@sss.pgh.pa.us>
|
|
wrote:
|
|
>Manfred Koizar <mkoi-pg@aon.at> writes:
|
|
>> Oracle basically supports (with slight variations between releases
|
|
>> 7/8/9):
|
|
>> DELETE [FROM] { table
|
|
>> | view
|
|
>> | ( subquery )
|
|
>> }
|
|
>> [alias] [WHERE ...] [returning_clause]
|
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>
|
|
>Bizarre. How are you supposed to delete from a subquery?
|
|
|
|
Hey, don't blame *me* :-) The thought seems to be, if it is ok to
|
|
delete from a view, and a view is just a name for a query, why not
|
|
allow to delete from a query. Here is an example out of the reference
|
|
manual:
|
|
DELETE FROM (select * from emp)
|
|
WHERE JOB = 'SALESMAN'
|
|
AND COMM < 100;
|
|
|
|
To be clear: I do *not* think, we need this in PostgreSQL. Otherwise
|
|
we'd also have to support delete from the result set of a function ;-)
|
|
|
|
BTW, I did some more digging. The results are somewhat confusing.
|
|
|
|
O7: no subquery
|
|
|
|
O8 v8.0: subquery allowed
|
|
|
|
O8i v8.1.5:
|
|
DELETE [ FROM ] table_expression_clause [ where_clause ]
|
|
|
|
table_expression_clause ::=
|
|
{ schema . { table
|
|
| view
|
|
| snapshot
|
|
}
|
|
| ( subquery )
|
|
| table_collection_expression
|
|
} [ , ... ]
|
|
|
|
Note, the syntax diagram in the "Oracle8i SQL Reference" claims, that
|
|
table_expression_clause can contain more than one table, view, etc.
|
|
but this feature(?) is not mentioned in the text. Please, could
|
|
someone try this?
|
|
|
|
O9i: only one table, view, ...
|
|
DELETE [hint] [FROM]
|
|
{ dml_table_expression_clause
|
|
| ONLY ( dml_table_expression_clause ) }
|
|
[t_alias] [where_clause] [returning_clause];
|
|
|
|
dml_table_expression_clause ::=
|
|
{ [schema .]
|
|
{ table
|
|
[ { PARTITION ( partition )
|
|
| SUBPARTITION ( subpartition ) }
|
|
| @ dblink
|
|
]
|
|
| { view | materialized view } [@ dblink]
|
|
}
|
|
| ( subquery [subquery_restriction_clause] )
|
|
| table_collection_expression
|
|
}
|
|
|
|
One more thing I found:
|
|
|
|
Informix XPS (Extended Parallel Server) v8.3 and later allows
|
|
|
|
DELETE FROM { table | view | synonym }
|
|
[ { USING | FROM }
|
|
{ table | view | synonym | alias } [ , ... ] ]
|
|
[ WHERE condition ]
|
|
|
|
which looks pretty much like your suggestion. Though the semantics
|
|
are a bit fuzzy. They require the target table to be listed after the
|
|
USING (or second FROM) keyword and give this example:
|
|
|
|
DELETE FROM lineitem
|
|
USING order o, lineitem l
|
|
WHERE o.qty < 1 AND o.order_num = l.order_num
|
|
|
|
But what would they do on
|
|
|
|
DELETE FROM lineitem
|
|
USING lineitem l1, lineitem l2
|
|
WHERE l1.item_num < l2.item_num
|
|
AND l1.order_num = l2.order_num
|
|
|
|
Servus
|
|
Manfred
|
|
|
|
---------------------------(end of broadcast)---------------------------
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TIP 5: Have you checked our extensive FAQ?
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http://www.postgresql.org/users-lounge/docs/faq.html
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From tgl@sss.pgh.pa.us Mon Jun 10 16:34:03 2002
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Return-path: <tgl@sss.pgh.pa.us>
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Mon, 10 Jun 2002 16:34:02 -0400 (EDT)
|
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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
|
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Subject: Re: [HACKERS] [SQL] 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>
|
|
Status: ORr
|
|
|
|
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
|
|
|
|
From pgsql-hackers-owner+M23590@postgresql.org Mon Jun 10 19:01:54 2002
|
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Return-path: <pgsql-hackers-owner+M23590@postgresql.org>
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From: Josh Berkus <josh@agliodbs.com>
|
|
Reply-To: josh@agliodbs.com
|
|
Organization: Aglio Database Solutions
|
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To: Tom Lane <tgl@sss.pgh.pa.us>, Manfred Koizar <mkoi-pg@aon.at>
|
|
Subject: Re: [HACKERS] [SQL] Efficient DELETE Strategies
|
|
Date: Mon, 10 Jun 2002 15:41:37 -0700
|
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X-Mailer: KMail [version 1.4]
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cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org,
|
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pgsql-hackers@postgresql.org
|
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References: <200206101142.NAA16854@rodos> <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com> <8806.1023743276@sss.pgh.pa.us>
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|
|
Status: OR
|
|
|
|
|
|
Tom,
|
|
|
|
> >> If so, what's their syntax?
|
|
>
|
|
> > MSSQL seems to guess what the user wants.
|
|
>
|
|
> Gack. Nothing like treating mindless syntax variations as a "feature"
|
|
> list...
|
|
|
|
I vote that we stick to a strick SQL92 interpretation, here.
|
|
1) It's standard
|
|
2) Strict syntax on DELETE statements is better.
|
|
|
|
Personally, I would *not* want the database to "guess what I want" in a delete
|
|
statement; it might guess wrong and there go my records ...
|
|
|
|
Heck, one of the things I need to research how to turn off in PostgreSQL is
|
|
the "Add missing FROM-clause" feature, which has tripped me up many times.
|
|
|
|
--
|
|
-Josh Berkus
|
|
|
|
|
|
---------------------------(end of broadcast)---------------------------
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TIP 4: Don't 'kill -9' the postmaster
|
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From pgsql-hackers-owner+M23592@postgresql.org Mon Jun 10 19:13:15 2002
|
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Subject: Re: [HACKERS] [SQL] Efficient DELETE Strategies
|
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MIME-Version: 1.0
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Date: Mon, 10 Jun 2002 16:08:03 -0700
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Message-ID: <D90A5A6C612A39408103E6ECDD77B82920CF3C@voyager.corporate.connx.com>
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Thread-Topic: [HACKERS] [SQL] Efficient DELETE Strategies
|
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Thread-Index: AcIQ0uZZci4VmpxkQ9O1oJ5J+ESqPgAAHBlQ
|
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From: "Dann Corbit" <DCorbit@connx.com>
|
|
To: <josh@agliodbs.com>, "Tom Lane" <tgl@sss.pgh.pa.us>,
|
|
"Manfred Koizar" <mkoi-pg@aon.at>
|
|
cc: "Christoph Haller" <ch@rodos.fzk.de>, <pgsql-sql@postgresql.org>,
|
|
<pgsql-hackers@postgresql.org>
|
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Precedence: bulk
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Status: OR
|
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|
|
> -----Original Message-----
|
|
> From: Josh Berkus [mailto:josh@agliodbs.com]
|
|
> Sent: Monday, June 10, 2002 3:42 PM
|
|
> To: Tom Lane; Manfred Koizar
|
|
> Cc: Christoph Haller; pgsql-sql@postgresql.org;
|
|
> pgsql-hackers@postgresql.org
|
|
> Subject: Re: [HACKERS] [SQL] Efficient DELETE Strategies
|
|
>
|
|
> Tom,
|
|
>
|
|
> > >> If so, what's their syntax?
|
|
> >
|
|
> > > MSSQL seems to guess what the user wants.
|
|
> >
|
|
> > Gack. Nothing like treating mindless syntax variations as
|
|
> a "feature"
|
|
> > list...
|
|
>
|
|
> I vote that we stick to a strick SQL92 interpretation, here.
|
|
> 1) It's standard
|
|
> 2) Strict syntax on DELETE statements is better.
|
|
>
|
|
> Personally, I would *not* want the database to "guess what I
|
|
> want" in a delete
|
|
> statement; it might guess wrong and there go my records ...
|
|
>
|
|
> Heck, one of the things I need to research how to turn off in
|
|
> PostgreSQL is
|
|
> the "Add missing FROM-clause" feature, which has tripped me
|
|
> up many times.
|
|
|
|
Agree strongly.
|
|
|
|
I would be very annoyed at any database system that guesses about what I
|
|
might want. It might guess wrong and cause enormous damage. It does
|
|
not have to be an update or delete for this damage to occur. It could
|
|
be a report that financial decisions were based upon. If someone does
|
|
get the PostgreSQL group to alter incoming statements, surely this
|
|
deserves *AT LEAST* a powerful warning message.
|
|
|
|
---------------------------(end of broadcast)---------------------------
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TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
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From pgsql-hackers-owner+M23595@postgresql.org Mon Jun 10 22:54:16 2002
|
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To: Hannu Krosing <hannu@tm.ee>
|
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cc: Tom Lane <tgl@sss.pgh.pa.us>, Christoph Haller <ch@rodos.fzk.de>,
|
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pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
|
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Subject: Re: [HACKERS] [SQL] Efficient DELETE Strategies
|
|
References: <200206101142.NAA16854@rodos> <5619.1023717387@sss.pgh.pa.us> <1023730428.4092.64.camel@taru.tm.ee>
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Status: OR
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|
|
This
|
|
|
|
Hannu Krosing wrote:
|
|
> DELETE relation_expr FROM relation_expr [ , table_ref [ , ... ] ]
|
|
> [ WHERE bool_expr ]
|
|
|
|
|
|
This in some ways is similar to Oracle where the FROM is optional in a
|
|
DELETE (ie. DELETE foo WHERE ...). By omitting the first FROM, the
|
|
syntax ends up mirroring the UPDATE case:
|
|
|
|
DELETE foo FROM bar WHERE ...
|
|
|
|
UPDATE foo FROM bar WHERE ...
|
|
|
|
However I think the syntax should also support the first FROM as being
|
|
optional (even though it looks confusing):
|
|
|
|
DELETE FROM foo FROM bar WHERE ...
|
|
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thanks,
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--Barry
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---------------------------(end of broadcast)---------------------------
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From pgsql-sql-owner+M8091=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 23:24:20 2002
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for pgsql-sql@postgresql.org; Tue, 11 Jun 2002 11:18:12 +0800 (WST)
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Tue, 11 Jun 2002 11:18:06 +0800 (WST)
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From: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
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To: "Tom Lane" <tgl@sss.pgh.pa.us>, "Manfred Koizar" <mkoi-pg@aon.at>
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cc: "Christoph Haller" <ch@rodos.fzk.de>, <pgsql-sql@postgresql.org>,
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<pgsql-hackers@postgresql.org>
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Subject: Re: [HACKERS] [SQL] Efficient DELETE Strategies
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Date: Tue, 11 Jun 2002 11:18:09 +0800
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Message-ID: <GNELIHDDFBOCMGBFGEFOMEKPCCAA.chriskl@familyhealth.com.au>
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Status: OR
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> Given the plethora of mutually incompatible interpretations that MSSQL
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> evidently supports, though, I fear we can't use it as precedent for
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> making any choices :-(.
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>
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> Can anyone check out other systems?
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MySQL:
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6.4.6 DELETE Syntax
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DELETE [LOW_PRIORITY | QUICK] FROM table_name
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[WHERE where_definition]
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[ORDER BY ...]
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[LIMIT rows]
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or
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DELETE [LOW_PRIORITY | QUICK] table_name[.*] [,table_name[.*] ...]
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FROM table-references
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[WHERE where_definition]
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or
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DELETE [LOW_PRIORITY | QUICK]
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FROM table_name[.*], [table_name[.*] ...]
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USING table-references
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[WHERE where_definition]
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DELETE deletes rows from table_name that satisfy the condition given by
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where_definition, and returns the number of records deleted.
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If you issue a DELETE with no WHERE clause, all rows are deleted. If you do
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this in AUTOCOMMIT mode, this works as TRUNCATE. See section 6.4.7 TRUNCATE
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Syntax. In MySQL 3.23, DELETE without a WHERE clause will return zero as the
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number of affected records.
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If you really want to know how many records are deleted when you are
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deleting all rows, and are willing to suffer a speed penalty, you can use a
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DELETE statement of this form:
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mysql> DELETE FROM table_name WHERE 1>0;
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Note that this is much slower than DELETE FROM table_name with no WHERE
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clause, because it deletes rows one at a time.
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If you specify the keyword LOW_PRIORITY, execution of the DELETE is delayed
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until no other clients are reading from the table.
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If you specify the word QUICK then the table handler will not merge index
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leaves during delete, which may speed up certain kind of deletes.
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In MyISAM tables, deleted records are maintained in a linked list and
|
|
subsequent INSERT operations reuse old record positions. To reclaim unused
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space and reduce file-sizes, use the OPTIMIZE TABLE statement or the
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|
myisamchk utility to reorganise tables. OPTIMIZE TABLE is easier, but
|
|
myisamchk is faster. See section 4.5.1 OPTIMIZE TABLE Syntax and section
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|
4.4.6.10 Table Optimisation.
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The first multi-table delete format is supported starting from MySQL 4.0.0.
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The second multi-table delete format is supported starting from MySQL 4.0.2.
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The idea is that only matching rows from the tables listed before the FROM
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or before the USING clause are deleted. The effect is that you can delete
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rows from many tables at the same time and also have additional tables that
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are used for searching.
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The .* after the table names is there just to be compatible with Access:
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DELETE t1,t2 FROM t1,t2,t3 WHERE t1.id=t2.id AND t2.id=t3.id
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or
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DELETE FROM t1,t2 USING t1,t2,t3 WHERE t1.id=t2.id AND t2.id=t3.id
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In the above case we delete matching rows just from tables t1 and t2.
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ORDER BY and using multiple tables in the DELETE statement is supported in
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MySQL 4.0.
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If an ORDER BY clause is used, the rows will be deleted in that order. This
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|
is really only useful in conjunction with LIMIT. For example:
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DELETE FROM somelog
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WHERE user = 'jcole'
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ORDER BY timestamp
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LIMIT 1
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This will delete the oldest entry (by timestamp) where the row matches the
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WHERE clause.
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The MySQL-specific LIMIT rows option to DELETE tells the server the maximum
|
|
number of rows to be deleted before control is returned to the client. This
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|
can be used to ensure that a specific DELETE command doesn't take too much
|
|
time. You can simply repeat the DELETE command until the number of affected
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rows is less than the LIMIT value.
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|
|
Chris
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---------------------------(end of broadcast)---------------------------
|
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TIP 6: Have you searched our list archives?
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|
http://archives.postgresql.org
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|
|
From pgsql-hackers-owner+M23605@postgresql.org Tue Jun 11 05:02:57 2002
|
|
Return-path: <pgsql-hackers-owner+M23605@postgresql.org>
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by candle.pha.pa.us (8.11.6/8.10.1) with ESMTP id g5B92vs09703
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for <pgman@candle.pha.pa.us>; Tue, 11 Jun 2002 05:02:57 -0400 (EDT)
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Received: from localhost.localdomain (postgresql.org [64.49.215.8])
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by localhost (Postfix) with ESMTP
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id 2D83C4760C4; Tue, 11 Jun 2002 05:02:53 -0400 (EDT)
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id 64E82475B2B; Tue, 11 Jun 2002 05:02:22 -0400 (EDT)
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Received: from taru.tm.ee (unknown [213.180.2.168])
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id 25B51475AF9; Tue, 11 Jun 2002 05:02:21 -0400 (EDT)
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Received: (from hannu@localhost)
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Tue, 11 Jun 2002 12:02:49 +0200
|
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X-Authentication-Warning: taru.tm.ee: hannu set sender to hannu@tm.ee using -f
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Subject: Re: [HACKERS] [SQL] 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
|
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Message-ID: <1023789769.6942.44.camel@taru.tm.ee>
|
|
MIME-Version: 1.0
|
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Sender: pgsql-hackers-owner@postgresql.org
|
|
Status: OR
|
|
|
|
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 [ , ... ] ]
|
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> > >> [ WHERE bool_expr ]
|
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> > >>
|
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> > >> or
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> > >>
|
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> > >> DELETE relation_expr.* FROM relation_expr [ , table_ref [ , ... ] ]
|
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> > >> [ WHERE bool_expr ]
|
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> >
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> > > So make the initial FROM optional and allow the later FROM to be a list
|
|
> > > of relations? Seems kind of strange.
|
|
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|
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
|
|
|
|
|
|
---------------------------(end of broadcast)---------------------------
|
|
TIP 3: if posting/reading through Usenet, please send an appropriate
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