mirror of https://github.com/postgres/postgres
Add delete selfjoin item.
This commit is contained in:
Bruce Momjian
parent
89f4f4a8e5
commit
566cde8cdc
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@ -0,0 +1,847 @@
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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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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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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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Status: ORr
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Christoph Haller <ch@rodos.fzk.de> writes:
|
||||
> Based on an entry in the mailing list from 30 Oct 2001
|
||||
> about efficient deletes on subqueries,
|
||||
> I've found two ways to do so (PostgreSQL 7.2.1):
|
||||
> ...
|
||||
> Is there a way to put the second form (more complicated, but faster)
|
||||
> 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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|
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regards, tom lane
|
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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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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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|
||||
Mon, 10 Jun 2002 17:07:56 -0400 (EDT)
|
||||
To: Manfred Koizar <mkoi-pg@aon.at>
|
||||
cc: Christoph Haller <ch@rodos.fzk.de>, pgsql-sql@postgresql.org,
|
||||
pgsql-hackers@postgresql.org
|
||||
Subject: Re: [SQL] Efficient DELETE Strategies
|
||||
In-Reply-To: <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com>
|
||||
References: <200206101142.NAA16854@rodos> <5619.1023717387@sss.pgh.pa.us> <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com>
|
||||
Comments: In-reply-to Manfred Koizar <mkoi-pg@aon.at>
|
||||
message dated "Mon, 10 Jun 2002 22:23:38 +0200"
|
||||
Date: Mon, 10 Jun 2002 17:07:56 -0400
|
||||
Message-ID: <8806.1023743276@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:
|
||||
>> 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...
|
||||
|
||||
> All the following statements do the same:
|
||||
|
||||
> (1) DELETE t1 FROM t2 WHERE t1.i=t2.i
|
||||
> (2a) DELETE t1 FROM t2, t1 WHERE t1.i=t2.i
|
||||
> (5) DELETE t1 FROM t1 a
|
||||
> WHERE EXISTS (SELECT * FROM t2 WHERE a.i=t2.i)
|
||||
> (6) DELETE a FROM t1 a WHERE EXISTS (SELECT * FROM t2 WHERE a.i=t2.i)
|
||||
|
||||
So in other words, MSSQL has no idea whether the name following DELETE
|
||||
is a real table name or an alias, and it's also unclear whether the name
|
||||
appears in the separate FROM clause or generates a FROM-item all by
|
||||
itself. This is why they have to punt on these cases:
|
||||
|
||||
> These don't work:
|
||||
> DELETE t1 FROM t1 b WHERE 2 * b.i = t1.i
|
||||
> "The column prefix 't1' does not match with a table name or alias name
|
||||
> used in the query."
|
||||
|
||||
> DELETE t1 FROM t1 a, t1 b WHERE 2 * b.i = a.i
|
||||
> "The table 't1' is ambiguous."
|
||||
|
||||
The ambiguity is entirely self-inflicted...
|
||||
|
||||
> And as if there aren't enough ways yet, I just discovered that (1) to
|
||||
> (6) just as much work with "DELETE FROM" where I wrote "DELETE" ...
|
||||
|
||||
Hm. So (1) with the DELETE FROM corresponds exactly to what I was
|
||||
suggesting:
|
||||
DELETE FROM t1 FROM t2 WHERE t1.i=t2.i
|
||||
except that I'd also allow an alias in there:
|
||||
DELETE FROM t1 a FROM t2 b WHERE a.i=b.i
|
||||
|
||||
Given the plethora of mutually incompatible interpretations that MSSQL
|
||||
evidently supports, though, I fear we can't use it as precedent for
|
||||
making any choices :-(.
|
||||
|
||||
Can anyone check out other systems?
|
||||
|
||||
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
|
||||
Return-path: <pgsql-sql-owner+M8093=candle.pha.pa.us=pgman@postgresql.org>
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|
||||
From: Christoph Haller <ch@rodos.fzk.de>
|
||||
Message-ID: <200206110918.LAA20463@rodos>
|
||||
Subject: Re: [SQL] Efficient DELETE Strategies
|
||||
To: pgsql-sql@postgresql.org
|
||||
Date: Tue, 11 Jun 2002 11:18:34 METDST
|
||||
X-Mailer: Elm [revision: 212.4]
|
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Precedence: bulk
|
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Sender: pgsql-sql-owner@postgresql.org
|
||||
Status: OR
|
||||
|
||||
Bruce Momjian wrote:
|
||||
> ...
|
||||
> Yes, another keyword is the only solution. Having FROM after DELETE
|
||||
> mean something different from FROM after a tablename is just too weird.
|
||||
> I know UPDATE uses FROM, and it is logical to use it here, but it is
|
||||
> just too wierd when DELETE already has a FROM. Should we allow FROM and
|
||||
> add WITH to UPDATE as well, and document WITH but support FROM too? No
|
||||
> idea. What if we support ADD FROM as the keywords for the new clause?
|
||||
|
||||
Sounds like the best solution so far.
|
||||
|
||||
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 ) ?
|
||||
And it looks like very much work for the HACKERS.
|
||||
|
||||
Hannu Krosing wrote:
|
||||
> ...
|
||||
> 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
|
||||
|
||||
This is a fine idea. But it looks like very much work for the HACKERS, too.
|
||||
|
||||
Regards, Christoph
|
||||
|
||||
---------------------------(end of broadcast)---------------------------
|
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|
||||
|
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From pgsql-sql-owner+M8094=candle.pha.pa.us=pgman@postgresql.org Tue Jun 11 10:29:20 2002
|
||||
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)
|
||||
To: Christoph Haller <ch@rodos.fzk.de>
|
||||
cc: pgsql-sql@postgresql.org
|
||||
Subject: Re: [SQL] Efficient DELETE Strategies
|
||||
In-Reply-To: <200206110918.LAA20463@rodos>
|
||||
References: <200206110918.LAA20463@rodos>
|
||||
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
|
||||
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
|
||||
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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|
||||
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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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Return-path: <pgsql-sql-owner+M8112=candle.pha.pa.us=pgman@postgresql.org>
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|
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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
|
||||
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
|
||||
|
||||
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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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 )
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> }
|
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> [alias] [WHERE ...] [returning_clause]
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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
|
||||
|
||||
---------------------------(end of broadcast)---------------------------
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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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for <tgl@sss.pgh.pa.us>; 12 Jun 2002 18:06:47 -0000
|
||||
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 20:06:11 +0200
|
||||
Message-ID: <dgqeguc0kf8ord0g37vo3hm6maqk649jak@4ax.com>
|
||||
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
|
||||
|
||||
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]
|
||||
>
|
||||
>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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|
||||
|
||||
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|
||||
|
||||
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Reference in New Issue