From 566cde8cdc44d812247da1285dfd77b6f02b0799 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <bruce@momjian.us>
Date: Mon, 26 Aug 2002 21:35:01 +0000
Subject: [PATCH] Add delete selfjoin item.
---
doc/TODO.detail/delete | 847 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 847 insertions(+)
create mode 100644 doc/TODO.detail/delete
diff --git a/doc/TODO.detail/delete b/doc/TODO.detail/delete
new file mode 100644
index 00000000000..10631a57034
--- /dev/null
+++ b/doc/TODO.detail/delete
@@ -0,0 +1,847 @@
+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>
+Message-ID: <200206101142.NAA16854@rodos>
+Subject: [SQL] Efficient DELETE Strategies
+To: pgsql-sql@postgresql.org
+Date: Mon, 10 Jun 2002 13:42:10 METDST
+X-Mailer: Elm [revision: 212.4]
+Precedence: bulk
+Sender: pgsql-sql-owner@postgresql.org
+Status: OR
+
+Hi,
+
+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):
+
+1.
+BEGIN ;
+EXPLAIN ANALYZE
+DELETE FROM onfvalue WHERE EXISTS(
+SELECT * FROM onfvalue j WHERE
+j.sid= 5 AND
+onfvalue.lid = j.lid AND
+onfvalue.mid = j.mid AND
+onfvalue.timepoint = j.timepoint AND
+onfvalue.entrancetime < j.entrancetime
+) ;
+ROLLBACK ;
+QUERY PLAN:
+
+Seq Scan on onfvalue
+(cost=0.00..805528.05 rows=66669 width=6)
+(actual time=61.84..25361.82 rows=24 loops=1)
+ SubPlan
+ -> Index Scan using advncd_onfvalue_idx_stlme on onfvalue j
+ (cost=0.00..6.02 rows=1 width=36)
+ (actual time=0.14..0.14 rows=0 loops=133338)
+Total runtime: 25364.76 msec
+
+2.
+BEGIN ;
+EXPLAIN ANALYZE
+INSERT INTO temprefentrancetime(timepoint,lid,mid,sid,entrancetime)
+SELECT o.timepoint,o.lid,o.mid,o.sid,o.entrancetime
+FROM onfvalue o join onfvalue j ON (
+o.lid = j.lid AND
+o.mid = j.mid AND
+o.timepoint = j.timepoint AND
+o.entrancetime < j.entrancetime
+) WHERE o.sid= 5 ;
+EXPLAIN ANALYZE
+DELETE FROM onfvalue WHERE
+onfvalue.timepoint = temprefentrancetime.timepoint AND
+onfvalue.mid = temprefentrancetime.mid AND
+onfvalue.lid = temprefentrancetime.lid AND
+onfvalue.sid = temprefentrancetime.sid AND
+onfvalue.entrancetime = temprefentrancetime.entrancetime ;
+DELETE FROM temprefentrancetime;
+ROLLBACK ;
+QUERY PLAN:
+
+Merge Join
+(cost=16083.12..16418.36 rows=4 width=52)
+(actual time=17728.06..19325.02 rows=24 loops=1)
+ -> Sort
+ (cost=2152.53..2152.53 rows=667 width=28)
+ (actual time=1937.70..2066.46 rows=16850 loops=1)
+ -> Index Scan using advncd_onfvalue_idx_stlme on onfvalue o
+ (cost=0.00..2121.26 rows=667 width=28)
+ (actual time=0.57..709.89 rows=16850 loops=1)
+ -> Sort
+ (cost=13930.60..13930.60 rows=133338 width=24)
+ (actual time=13986.07..14997.43 rows=133110 loops=1)
+ -> Seq Scan on onfvalue j
+ (cost=0.00..2580.38 rows=133338 width=24)
+ (actual time=0.15..3301.06 rows=133338 loops=1)
+Total runtime: 19487.49 msec
+
+QUERY PLAN:
+
+Nested Loop
+(cost=0.00..6064.40 rows=1 width=62)
+(actual time=1.34..8.32 rows=24 loops=1)
+ -> Seq Scan on temprefentrancetime
+ (cost=0.00..20.00 rows=1000 width=28)
+ (actual time=0.44..1.07 rows=24 loops=1)
+ -> Index Scan using advncd_onfvalue_idx_stlme on onfvalue
+ (cost=0.00..6.02 rows=1 width=34)
+ (actual time=0.22..0.25 rows=1 loops=24)
+Total runtime: 10.15 msec
+
+The questions are:
+Is there a way to put the second form (more complicated, but faster)
+in one statement?
+Or is there even a third way to delete, which I cannot see?
+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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+ Mon, 10 Jun 2002 09:56:28 -0400 (EDT)
+To: Christoph Haller <ch@rodos.fzk.de>
+cc: pgsql-sql@postgresql.org, pgsql-hackers@postgresql.org
+Subject: Re: [SQL] Efficient DELETE Strategies
+In-Reply-To: <200206101142.NAA16854@rodos>
+References: <200206101142.NAA16854@rodos>
+Comments: In-reply-to Christoph Haller <ch@rodos.fzk.de>
+ message dated "Mon, 10 Jun 2002 13:42:10 +0700"
+Date: Mon, 10 Jun 2002 09:56:27 -0400
+Message-ID: <5619.1023717387@sss.pgh.pa.us>
+From: Tom Lane <tgl@sss.pgh.pa.us>
+Precedence: bulk
+Sender: pgsql-sql-owner@postgresql.org
+Status: ORr
+
+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?
+> Or is there even a third way to delete, which I cannot see?
+
+The clean way to do this would be to allow extra FROM-list relations
+in DELETE. We already have a similar facility for UPDATE, so it's not
+clear to me why there's not one for DELETE. Then you could do, say,
+
+DELETE FROM onfvalue , onfvalue j WHERE
+j.sid= 5 AND
+onfvalue.lid = j.lid AND
+onfvalue.mid = j.mid AND
+onfvalue.timepoint = j.timepoint AND
+onfvalue.entrancetime < j.entrancetime ;
+
+If you were using two separate tables you could force this to happen
+via an implicit FROM-clause entry, much as you've done in your second
+alternative --- but there's no way to set up a self-join in a DELETE
+because of the lack of any place to put an alias declaration.
+
+AFAIK this extension would be utterly trivial to implement, since all
+the machinery is there already --- for 99% of the backend, it doesn't
+matter whether a FROM-item is implicit or explicit. We'd only need to
+argue out what the syntax should be. I could imagine
+
+ DELETE FROM relation_expr [ , table_ref [ , ... ] ]
+ [ WHERE bool_expr ]
+
+or
+
+ DELETE FROM relation_expr [ FROM table_ref [ , ... ] ]
+ [ WHERE bool_expr ]
+
+The two FROMs in the second form look a little weird, but they help to
+make a clear separation between the deletion target table and the
+merely-referenced tables. Also, the first one might look to people
+like they'd be allowed to write
+
+ DELETE FROM foo FULL JOIN bar ...
+
+which is not any part of my intention (it's very unclear what it'd
+mean for the target table to be on the nullable side of an outer join).
+OTOH there'd be no harm in outer joins in a separate from-clause, eg
+
+ DELETE FROM foo FROM (bar FULL JOIN baz ON ...) WHERE ...
+
+Actually, either syntax above would support that; I guess what's really
+bothering me about the first syntax is that a comma suggests a list of
+things that will all be treated similarly, while in reality the first
+item will be treated much differently from the rest.
+
+Does anyone know whether other systems that support the UPDATE extension
+for multiple tables also support a DELETE extension for multiple tables?
+If so, what's their syntax?
+
+A somewhat-related issue is that people keep expecting to be able to
+attach an alias to the target table name in UPDATE and DELETE; seems
+like we get that question every couple months. While this is clearly
+disallowed by the SQL spec, it's apparently supported by some other
+implementations (else we'd not get the question so much). Should we
+add that extension to our syntax? Or should we continue to resist it?
+
+ regards, tom lane
+
+---------------------------(end of broadcast)---------------------------
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+
+From pgsql-sql-owner+M8084=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 17:29:55 2002
+Return-path: <pgsql-sql-owner+M8084=candle.pha.pa.us=pgman@postgresql.org>
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+ for <tgl@sss.pgh.pa.us>; 10 Jun 2002 20:24:10 -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,
+ pgsql-hackers@postgresql.org
+Subject: Re: [SQL] Efficient DELETE Strategies
+Date: Mon, 10 Jun 2002 22:23:38 +0200
+Message-ID: <j8u9gukf7882nq3tsfhqr5bte9386p637l@4ax.com>
+References: <200206101142.NAA16854@rodos> <5619.1023717387@sss.pgh.pa.us>
+In-Reply-To: <5619.1023717387@sss.pgh.pa.us>
+X-Mailer: Forte Agent 1.8/32.548
+MIME-Version: 1.0
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+Sender: pgsql-sql-owner@postgresql.org
+Status: OR
+
+On Mon, 10 Jun 2002 09:56:27 -0400, Tom Lane <tgl@sss.pgh.pa.us>
+wrote:
+>Does anyone know whether other systems that support the UPDATE extension
+>for multiple tables also support a DELETE extension for multiple tables?
+>If so, what's their syntax?
+
+MSSQL seems to guess what the user wants. All the following
+statements do the same:
+
+(0) DELETE FROM t1 WHERE EXISTS (SELECT * FROM t2 WHERE t1.i=t2.i)
+(1) DELETE t1 FROM t2 WHERE t1.i=t2.i
+(2a) DELETE t1 FROM t2, t1 WHERE t1.i=t2.i
+(2b) DELETE t1 FROM t2 INNER JOIN t1 ON t1.i=t2.i
+(3a) DELETE t1 FROM t2, t1 a WHERE a.i=t2.i
+(3b) DELETE t1 FROM t2 INNER JOIN t1 a ON a.i=t2.i
+(4a) DELETE a FROM t2, t1 a WHERE a.i=t2.i
+(4b) DELETE a FROM t2 INNER JOIN t1 a ON a.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)
+
+(0) is standard SQL and should always work. As an extension I'd like
+(1) or (2), but only one of them and forbid the other one. I'd also
+forbid (3), don't know what to think of (4), and don't see a reason
+why we would want (5) or (6). I'd rather have (7) or (8).
+
+These don't work:
+(7) DELETE t1 a FROM t2 WHERE a.i = t2.i
+"Incorrect syntax near 'a'."
+
+(8) DELETE FROM t1 a WHERE EXISTS (SELECT * FROM t2 WHERE a.i = t2.i)
+"Incorrect syntax near 'a'."
+
+Self joins:
+(2as) DELETE t1 FROM t1, t1 b WHERE 2*b.i=t1.i
+(4as) DELETE a FROM t1 a, t1 b WHERE 2*b.i=a.i
+(4bs) DELETE a FROM t1 a INNER JOIN t1 b on 2*b.i=a.i
+
+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."
+
+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" ...
+
+Servus
+ Manfred
+
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+
+From pgsql-sql-owner+M8087=candle.pha.pa.us=pgman@postgresql.org Mon Jun 10 18:21:01 2002
+Return-path: <pgsql-sql-owner+M8087=candle.pha.pa.us=pgman@postgresql.org>
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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
+
+---------------------------(end of broadcast)---------------------------
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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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+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
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+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
+
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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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+ 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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+From pgsql-sql-owner+M8112=candle.pha.pa.us=pgman@postgresql.org Wed Jun 12 10:04:47 2002
+Return-path: <pgsql-sql-owner+M8112=candle.pha.pa.us=pgman@postgresql.org>
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+ for <tgl@sss.pgh.pa.us>; 12 Jun 2002 14:04:17 -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 16:03:39 +0200
+Message-ID: <es9eguk7ov9644qo4qd341ess8ip8o51ok@4ax.com>
+References: <200206110918.LAA20463@rodos> <18946.1023805720@sss.pgh.pa.us>
+In-Reply-To: <18946.1023805720@sss.pgh.pa.us>
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+Sender: pgsql-sql-owner@postgresql.org
+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
+Return-path: <pgsql-sql-owner+M8113=candle.pha.pa.us=pgman@postgresql.org>
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+ Wed, 12 Jun 2002 10:49:26 -0400 (EDT)
+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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+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>
+In-Reply-To: <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
+
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