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566cde8cdc
postgresql/doc/TODO.detail/delete
Bruce Momjian 566cde8cdc Add delete selfjoin item.
2002-08-26 21:35:01 +00:00

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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>
Message-ID: <200206101142.NAA16854@rodos>
Subject: [SQL] Efficient DELETE Strategies
To: pgsql-sql@postgresql.org
Date: Mon, 10 Jun 2002 13:42:10 METDST
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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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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>
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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?
> 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
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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>
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>
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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
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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>
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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
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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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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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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>
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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
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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>
References: <200206110918.LAA20463@rodos> <18946.1023805720@sss.pgh.pa.us>
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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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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>
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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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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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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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