1112 lines
47 KiB
Plaintext
1112 lines
47 KiB
Plaintext
From owner-pgsql-hackers@hub.org Tue Jun 1 22:31:18 1999
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for <pgsql-hackers@hub.org>; Tue, 1 Jun 1999 22:00:50 -0400 (EDT)
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(envelope-from chris.bitmead@bigfoot.com)
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for <pgsql-hackers@hub.org>; Wed, 2 Jun 1999 10:50:11 +1000
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Message-ID: <37547FC3.40106A5E@bigfoot.com>
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Date: Wed, 02 Jun 1999 10:50:11 +1000
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From: Chris Bitmead <chris.bitmead@bigfoot.com>
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MIME-Version: 1.0
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To: pgsql-hackers@hub.org
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Subject: Re: [HACKERS] ALTER TABLE ADD COLUMN
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References: <199906011436.KAA23479@candle.pha.pa.us>
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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Bruce Momjian wrote:
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> Our TODO now has:
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>
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> * ALTER TABLE ADD COLUMN to inherited table put column in wrong place
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>
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> I don't think any of us understand the issues on this one.
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Let me guess at the problem. When you add a column, it doesn't change
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all the records, therefore the column must be added at the end. This
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means that the columns will not be in the same order as if you had
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created them from scratch.
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There seem to be three solutions:
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a) Go to a much more sophisticated schema system, with versions and
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version numbers (fairly hard but desirable to fix other schema change
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problems). Then insert the column in the position it is supposed to be
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in.
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b) Fix the copy command to input and output the columns, not in the
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order they are in, but in the order they would be in on re-creation.
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c) make the copy command take arguments specifying the field names, like
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INSERT can do.
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I think it would be good if Postgres had all 3 features. Probably (b) is
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the least work.
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From owner-pgsql-general@hub.org Fri Jul 9 04:01:16 1999
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Message-ID: <000c01bec9df$3704bd20$0601a8c0@kosovo.idianet.net>
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Reply-To: "Jonathan davis" <haj@idianet.net>
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From: "Jonathan davis" <haj@idianet.net>
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To: "Bruce Momjian" <maillist@candle.pha.pa.us>
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Cc: "Pgsql-General@Postgresql. Org" <pgsql-general@postgreSQL.org>
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Subject: Re: [GENERAL] just little BUG
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Date: Fri, 9 Jul 1999 09:46:42 +0200
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Status: ROr
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>[Charset iso-8859-1 unsupported, filtering to ASCII...]
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>> hello all
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>>
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>> normaly a UNIQUE PRIMARY KEY is unique but
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>> when you use a heritage, you can insert a duplicate key !!!!
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>
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>I assume you mean inheritance.
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>
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>Can you send us a little test sample please?
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>
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>--
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hello all
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this is the problem:
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example:
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test=> CREATE TABLE MAN(name char(10) UNIQUE PRIMARY KEY);T
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test=> CREATE TABLE PROFESSOR(scool char(20))INHERITS(MAN);
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test=> INSERT INTO PROFESSOR(name) VALUES('DAVIS');
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INSERT 54424 1
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test=> INSERT INTO PROFESSOR(name) VALUES('DAVIS');
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INSERT 54425 1
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From owner-pgsql-hackers@hub.org Tue Apr 20 10:34:34 1999
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for <hackers@postgreSQL.org>; Tue, 20 Apr 1999 10:31:52 -0400 (EDT)
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(envelope-from chris.bitmead@bigfoot.com)
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for <hackers@postgreSQL.org>; Wed, 21 Apr 1999 00:31:32 +1000
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Message-ID: <371C8FC3.4804CF87@bigfoot.com>
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Date: Tue, 20 Apr 1999 14:31:31 +0000
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From: Chris Bitmead <chris.bitmead@bigfoot.com>
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To: hackers@postgreSQL.org
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Subject: Re: [HACKERS] Heads up: does RULES regress test still work for you?
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References: <199904151054.UAA07367@tech.com.au> <3715C69E.AE517ADB@bigfoot.com>
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Sender: owner-pgsql-hackers@postgreSQL.org
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Status: RO
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Does the following indicate a bug? It sure is wierd. Maybe some of these
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statements aren't supported by postgresql (??), but the outcome doesn't
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make sense to me.
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httpd=> CREATE TABLE x (y text);
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CREATE
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httpd=> CREATE VIEW z AS select * from x;
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CREATE
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httpd=> CREATE TABLE a (b text) INHERITS(z);
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CREATE
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httpd=> INSERT INTO x VALUES ('foo');
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INSERT 168602 1
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httpd=> select * from z*;
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y
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---
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foo
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foo
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(2 rows)
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How did we suddenly get two rows??
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--
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Chris Bitmead
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http://www.bigfoot.com/~chris.bitmead
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mailto:chris.bitmead@bigfoot.com
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From owner-pgsql-hackers@hub.org Tue May 25 11:01:16 1999
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for <pgsql-hackers@postgreSQL.org>; Tue, 25 May 1999 10:42:39 -0400 (EDT)
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To: pgsql-hackers@postgreSQL.org
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Subject: [HACKERS] INSERT INTO view means what exactly?
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Date: Tue, 25 May 1999 10:42:39 -0400
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Message-ID: <2981.927643359@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: ROr
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With current sources:
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regression=> CREATE TABLE x (y text);
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CREATE
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regression=> CREATE VIEW z AS select * from x;
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CREATE
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regression=> INSERT INTO x VALUES ('foo');
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INSERT 411635 1
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regression=> INSERT INTO z VALUES ('bar');
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INSERT 411636 1
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regression=> select * from x;
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y
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---
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foo
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(1 row)
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regression=> select * from z;
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y
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---
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foo
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(1 row)
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OK, where'd tuple 411636 go? Seems to me that the insert should either
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have been rejected or caused an insert into x, depending on how
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transparent you think views are (I always thought they were
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read-only?). Dropping the data into never-never land and giving a
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misleading success response code is not my idea of proper behavior.
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regards, tom lane
|
||
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||
|
||
From owner-pgsql-hackers@hub.org Mon Jan 24 23:46:25 2000
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Mon, 24 Jan 2000 22:57:12 -0500 (EST)
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To: Don Baccus <dhogaza@pacifier.com>
|
||
cc: "Hiroshi Inoue" <Inoue@tpf.co.jp>, "Peter Eisentraut" <peter_e@gmx.net>,
|
||
"PostgreSQL Development" <pgsql-hackers@postgreSQL.org>
|
||
Subject: Re: [HACKERS] Happy column dropping
|
||
In-reply-to: <3.0.1.32.20000124184137.01069490@mail.pacifier.com>
|
||
References: <001001bf66d7$b531ba00$2801007e@tpf.co.jp> <001001bf66d7$b531ba00$2801007e@tpf.co.jp> <3.0.1.32.20000124184137.01069490@mail.pacifier.com>
|
||
Comments: In-reply-to Don Baccus <dhogaza@pacifier.com>
|
||
message dated "Mon, 24 Jan 2000 18:41:37 -0800"
|
||
Date: Mon, 24 Jan 2000 22:57:12 -0500
|
||
Message-ID: <11573.948772632@sss.pgh.pa.us>
|
||
From: Tom Lane <tgl@sss.pgh.pa.us>
|
||
Sender: owner-pgsql-hackers@postgreSQL.org
|
||
Status: RO
|
||
|
||
Don Baccus <dhogaza@pacifier.com> writes:
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||
> Just a reality check for my learning of the internals. Out of curiousity
|
||
> I coincidently have spent the last hour looking to see how add column's
|
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> implemented. It doesn't appear to do anything other than the new attribute
|
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> to the proper system table. heap_getattr() just returns null if you ask
|
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> for an attribute past the end of the tuple.
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> This would appear to be (at least one reason) why you can't add a "not null"
|
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> constraint to a column you're adding to an existing relation, or set the
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> new column to some non-null default value.
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> Correct? (again, to see if my eyeballs and brain are working in synch
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> tonight)
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||
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Yup, that's about the size of it. ADD COLUMN doesn't actually touch the
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table itself, so it can only add a column that's initially all NULLs.
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And even this depends on some uncomfortable assumptions about the
|
||
robustness of heap_getattr(). I have always wondered whether it works
|
||
if you ADD COLUMN a 33'rd column (or anything that is just past the
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next padding boundary for the null-values bitmap).
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||
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||
Another problem with it is seen when you do a recursive ADD COLUMN in
|
||
an inheritance tree. The added column has the first free column number
|
||
in each table, which generally means that it has different numbers in
|
||
the children than in the parent. There are some kluges to make this
|
||
sort-of-work for simple cases, but a lot of stuff fails unpleasantly
|
||
--- Chris Bitmead can show you some scars from that, IIRC.
|
||
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> Does your comment imply that it's planned to change this, i.e. actually
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> add the new column to each tuple in the relation rather than use the
|
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> existing, somewhat elegant hack?
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That's what I would like to see: all the children should have the
|
||
same column numbers for all columns that they inherit from the parent.
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(Now, this would mean not only physically altering the tuples of
|
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the children, but also renumbering their added columns, which has
|
||
implications on stored rules and triggers and so forth. It'd be
|
||
painful, no doubt about it. Still, I'd rather pay the price in the
|
||
seldom-used ADD COLUMN case than try to deal with out-of-sync column
|
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numbers in many other, more commonly exercised, code paths.)
|
||
|
||
regards, tom lane
|
||
|
||
************
|
||
|
||
From owner-pgsql-hackers@hub.org Tue Jan 25 18:34:14 2000
|
||
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|
||
Message-ID: <388E3EE9.46880647@tm.ee>
|
||
Date: Wed, 26 Jan 2000 02:25:13 +0200
|
||
From: Hannu Krosing <hannu@tm.ee>
|
||
Organization: Trust-O-Matic =?iso-8859-1?Q?O=DC?=
|
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|
||
To: Don Baccus <dhogaza@pacifier.com>
|
||
Cc: Tom Lane <tgl@sss.pgh.pa.us>,
|
||
"Ross J. Reedstrom" <reedstrm@wallace.ece.rice.edu>,
|
||
PostgreSQL Development <pgsql-hackers@postgreSQL.org>
|
||
Subject: Re: Happy column adding (was RE: [HACKERS] Happy columndropping)
|
||
References: <3.0.1.32.20000125113001.00f8acb0@mail.pacifier.com>
|
||
<20000125114453.E423@rice.edu>
|
||
<001401bf6704$5ca7e3a0$2801007e@tpf.co.jp>
|
||
<Pine.GSO.4.02A.10001251152160.11899-100000@Val.DoCS.UU.SE>
|
||
<3.0.1.32.20000125080125.00f7f160@mail.pacifier.com>
|
||
<20000125114453.E423@rice.edu>
|
||
<3.0.1.32.20000125113001.00f8acb0@mail.pacifier.com> <3.0.1.32.20000125151022.00f8c4c0@mail.pacifier.com>
|
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|
||
Status: OR
|
||
|
||
Don Baccus wrote:
|
||
>
|
||
> Ahhh...yes. I haven't looked at the inheritance code, yet, but I see
|
||
> what you're saying. I think. Do child-table columns follow parent-table
|
||
> columns by some chance (in today's absolute column number scheme)?
|
||
>
|
||
> >If we were willing to hardwire the assumption that DROP COLUMN never
|
||
> >physically drops a column, but only hides it and adjusts logical column
|
||
> >numbers, then the physical column numbers could serve as permanent IDs;
|
||
> >so we'd only need two numbers not three. This might be good, or not.
|
||
>
|
||
> Yes. But if I'm right about how child-table columns are numbered,
|
||
> wouldn't add column still cause a problem, i.e. you'd still have to
|
||
> change their physical column number?
|
||
|
||
If we allow deleted column as a basic feature of postgres,
|
||
it could be like that
|
||
|
||
base: COL1 | COL2 | COL3
|
||
child: COL1 | COL2 | COL3 | COL4
|
||
|
||
after add column 5 to base table
|
||
|
||
base: COL1 | COL2 | COL3 | del4 | COL5
|
||
child: COL1 | COL2 | COL3 | COL4 | COL5
|
||
|
||
after add column 6 to child
|
||
|
||
base: COL1 | COL2 | COL3 | del4 | COL5
|
||
child: COL1 | COL2 | COL3 | COL4 | COL5 | COL6
|
||
|
||
after drop column 2 from base table
|
||
|
||
base: COL1 | del2 | COL3 | del4 | COL5
|
||
child: COL1 | del2 | COL3 | COL4 | COL5 | COL6
|
||
|
||
dropping column from child table that is not a deleted column in
|
||
parent is not allowed.
|
||
|
||
The delN columns are always NULLed on reading tuple and are written as proper
|
||
null columns (taking up space only in NULL bitmask)
|
||
|
||
multiple inheritance is tricky and _requires_ unique column ids maybe oids
|
||
from pg_attribute to be doable.
|
||
|
||
-----------------
|
||
Hannu
|
||
|
||
************
|
||
|
||
From owner-pgsql-hackers@hub.org Thu Jan 27 11:48:26 2000
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||
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id 12DsvR-0000HH-00; Thu, 27 Jan 2000 18:41:45 +0100
|
||
Date: Thu, 27 Jan 2000 18:41:45 +0100 (CET)
|
||
From: Peter Eisentraut <peter_e@gmx.net>
|
||
To: Tom Lane <tgl@sss.pgh.pa.us>
|
||
cc: PostgreSQL Development <pgsql-hackers@postgreSQL.org>
|
||
Subject: Re: [HACKERS] Column ADDing issues
|
||
In-Reply-To: <15550.948845404@sss.pgh.pa.us>
|
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Message-ID: <Pine.LNX.4.21.0001262020480.416-100000@localhost.localdomain>
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|
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Status: ORr
|
||
|
||
On 2000-01-25, Tom Lane mentioned:
|
||
|
||
> > Everything has its order and it's not like the inheritance as such is
|
||
> > broken.
|
||
>
|
||
> Yes, a whole bunch of stuff is broken after this happens. Go back and
|
||
> consult the archives --- or maybe Chris Bitmead will fill you in; he's
|
||
> got plenty of scars to show for this set of problems. (All I recall
|
||
> offhand is that pg_dump and reload can fail to generate a working
|
||
> database.) The bottom line is that it would be a lot nicer if column c
|
||
> had the same column position in both the parent table and the child
|
||
> table(s).
|
||
|
||
This should be fixed in pg_dump by infering something via the oids of the
|
||
pg_attribute entries. No need to mess up the backend for it.
|
||
|
||
Maybe pg_dump should optionally dump schemas in terms of insert into
|
||
pg_something commands rather than actual DDL. ;)
|
||
|
||
>
|
||
> I suggest you be very cautious about messing with ALTER TABLE until you
|
||
> understand why inheritance makes it such a headache ;-)
|
||
|
||
I'm just trying to get the defaults and constraints working. If
|
||
inheritance stays broken the way it previously was, it's beyond my
|
||
powers. But I get the feeling that people rather not alter their tables
|
||
unless they have *perfect* alter table commands. I don't feel like arguing
|
||
with them, they'll just have to do without then.
|
||
|
||
|
||
--
|
||
Peter Eisentraut Sernanders v<>g 10:115
|
||
peter_e@gmx.net 75262 Uppsala
|
||
http://yi.org/peter-e/ Sweden
|
||
|
||
|
||
|
||
************
|
||
|
||
From pgsql-general-owner+M2136@hub.org Sat Jun 3 23:31:02 2000
|
||
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Date: Sun, 4 Jun 2000 03:46:53 +0200 (CEST)
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From: Peter Eisentraut <peter_e@gmx.net>
|
||
To: ldm@apartia.com
|
||
cc: pgsql-general@postgresql.org
|
||
Subject: Re: [GENERAL] child table doesn't inherit PRIMARY KEY?
|
||
In-Reply-To: <20000603172256.A3435@styx>
|
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Message-ID: <Pine.LNX.4.21.0006040341030.348-100000@localhost.localdomain>
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|
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Status: ORr
|
||
|
||
Louis-David Mitterrand writes:
|
||
|
||
> When creating a child (through CREATE TABLE ... INHERIT (parent)) it
|
||
> seems the child gets all of the parent's contraints _except_ its PRIMARY
|
||
> KEY. Is this normal?
|
||
|
||
It's kind of a bug.
|
||
|
||
|
||
--
|
||
Peter Eisentraut Sernanders v<>g 10:115
|
||
peter_e@gmx.net 75262 Uppsala
|
||
http://yi.org/peter-e/ Sweden
|
||
|
||
|
||
From sszabo@megazone23.bigpanda.com Fri Jan 19 12:37:34 2001
|
||
Received: from megazone23.bigpanda.com (rfx-64-6-210-138.users.reflexcom.com [64.6.210.138])
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Fri, 19 Jan 2001 09:37:03 -0800 (PST)
|
||
Date: Fri, 19 Jan 2001 09:37:02 -0800 (PST)
|
||
From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
|
||
To: Bruce Momjian <pgman@candle.pha.pa.us>
|
||
cc: pgsql-general@postgresql.org
|
||
Subject: Re: [GENERAL] child table doesn't inherit PRIMARY KEY?
|
||
In-Reply-To: <200101190457.XAA13895@candle.pha.pa.us>
|
||
Message-ID: <Pine.BSF.4.21.0101190932480.5520-100000@megazone23.bigpanda.com>
|
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MIME-Version: 1.0
|
||
Content-Type: TEXT/PLAIN; charset=US-ASCII
|
||
Status: OR
|
||
|
||
|
||
Probably, since I see it in near recent sources (and it affects
|
||
UNIQUE as well. As I remember it, the last discussion on this couldn't
|
||
determine what the correct behavior for unique/primary key constraints
|
||
was in the inheritance case (is it a single unique hierarchy through
|
||
all the tables [would be needed for fk to inheritance trees] or
|
||
separate unique constraints for each table [which would be similar
|
||
to how many people seem to currently use postgres inheritance as a
|
||
shortcut]).
|
||
|
||
On Thu, 18 Jan 2001, Bruce Momjian wrote:
|
||
|
||
> Does this bug still exist?
|
||
>
|
||
> [ Charset ISO-8859-1 unsupported, converting... ]
|
||
> > Louis-David Mitterrand writes:
|
||
> >
|
||
> > > When creating a child (through CREATE TABLE ... INHERIT (parent)) it
|
||
> > > seems the child gets all of the parent's contraints _except_ its PRIMARY
|
||
> > > KEY. Is this normal?
|
||
|
||
|
||
From sszabo@megazone23.bigpanda.com Wed Jan 24 14:26:12 2001
|
||
Received: from megazone23.bigpanda.com (rfx-64-6-210-138.users.reflexcom.com [64.6.210.138])
|
||
by candle.pha.pa.us (8.9.0/8.9.0) with ESMTP id OAA26091
|
||
for <pgman@candle.pha.pa.us>; Wed, 24 Jan 2001 14:26:10 -0500 (EST)
|
||
Received: from localhost (sszabo@localhost)
|
||
by megazone23.bigpanda.com (8.11.1/8.11.1) with ESMTP id f0OJPZ858086;
|
||
Wed, 24 Jan 2001 11:25:35 -0800 (PST)
|
||
Date: Wed, 24 Jan 2001 11:25:35 -0800 (PST)
|
||
From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
|
||
To: Bruce Momjian <pgman@candle.pha.pa.us>
|
||
cc: PostgreSQL-development <pgsql-hackers@postgreSQL.org>
|
||
Subject: Re: [GENERAL] child table doesn't inherit PRIMARY KEY?
|
||
In-Reply-To: <200101241344.IAA12094@candle.pha.pa.us>
|
||
Message-ID: <Pine.BSF.4.21.0101241120310.57849-100000@megazone23.bigpanda.com>
|
||
MIME-Version: 1.0
|
||
Content-Type: TEXT/PLAIN; charset=US-ASCII
|
||
Status: ORr
|
||
|
||
On Wed, 24 Jan 2001, Bruce Momjian wrote:
|
||
|
||
>
|
||
> OK, what do people want to do with this item? Add to TODO list?
|
||
>
|
||
> Seems making a separat unique constraint would be easy to do and be of
|
||
> value to most users.
|
||
|
||
The problem is that doing that will pretty much guarantee that we won't
|
||
be doing foreign keys to inheritance trees without changing that behavior
|
||
and we've seen people asking about adding that too. I think that this
|
||
falls into the general category of "Make inheritance make sense" (Now
|
||
there's a todo item :) ) Seriously, I think the work on how inheritance
|
||
is going to work will decide this, maybe we end up with a real inheritance
|
||
tree system and something that works like the current stuff in which case
|
||
I'd say it's probably one unique for the former and one per for the
|
||
latter.
|
||
|
||
|
||
|
||
|
||
From olly@lfix.co.uk Wed Jan 24 16:41:45 2001
|
||
Received: from anchor-post-31.mail.demon.net (anchor-post-31.mail.demon.net [194.217.242.89])
|
||
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|
||
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|
||
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|
||
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|
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|
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|
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|
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|
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|
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|
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|
||
p^e=Z.K~fuw$l?]lUV)?R]U}l;f*~Ol)#fpKR)Yt}XOr6BI\_Jjr0!@GMnpCTnTym4f;c{;Ms=0{`D
|
||
Lq9MO6{wj%s-*N"G,g
|
||
To: Bruce Momjian <pgman@candle.pha.pa.us>
|
||
cc: Stephan Szabo <sszabo@megazone23.bigpanda.com>,
|
||
PostgreSQL-development <pgsql-hackers@postgresql.org>
|
||
Subject: Re: [HACKERS] Re: [GENERAL] child table doesn't inherit PRIMARY KEY?
|
||
In-reply-to: Message from Bruce Momjian <pgman@candle.pha.pa.us>
|
||
of Wed, 24 Jan 2001 14:31:29 EST. <200101241931.OAA26463@candle.pha.pa.us>
|
||
Mime-Version: 1.0
|
||
Content-Type: text/plain; charset=us-ascii
|
||
Date: Wed, 24 Jan 2001 21:41:39 +0000
|
||
From: "Oliver Elphick" <olly@lfix.co.uk>
|
||
Status: OR
|
||
|
||
Bruce Momjian wrote:
|
||
>> On Wed, 24 Jan 2001, Bruce Momjian wrote:
|
||
|
||
>I smell TODO item. In fact, I now see a TODO item:
|
||
>
|
||
>* Unique index on base column not honored on inserts from inherited table
|
||
> INSERT INTO inherit_table (unique_index_col) VALUES (dup) should fail
|
||
> [inherit]
|
||
>
|
||
>So it seems the fact the UNIQUE doesn't apply to the new table is just a
|
||
>manifestion of the fact that people expect UNIQUE to span the entire
|
||
>inheritance tree. I will add the emails to [inherit] and mark it as
|
||
>resolved.
|
||
|
||
Bruce, could you add this text to TODO.detail on the subject of
|
||
inherited constraints. I first sent it on Christmas Eve, and I
|
||
think most people were too busy holidaying to comment.
|
||
|
||
=================================================================
|
||
Tom Lane wrote:
|
||
>Hm. The short-term answer seems to be to modify the queries generated
|
||
>by the RI triggers to say "ONLY foo". I am not sure whether we
|
||
>understand the semantics involved in allowing a REFERENCES target to be
|
||
>taken as an inheritance tree rather than just one table, but certainly
|
||
>the current implementation won't handle that correctly.
|
||
|
||
May I propose these semantics as a basis for future development:
|
||
|
||
1. An inheritance hierarchy (starting at any point in a tree) should be
|
||
equivalent to an updatable view of all the tables at the point of
|
||
reference and below. By default, all descendant tables are combined
|
||
with the ancestor for all purposes. The keyword ONLY must be used to
|
||
alter this behaviour. Only inherited columns of descendant tables are
|
||
visible from higher in the tree. Columns may not be dropped in descendants.
|
||
If columns are added to ancestors, they must be inserted correctly in
|
||
descendants so as to preserve column ordering and inheritance. If
|
||
a column is dropped in an ancestor, it is dropped in all descendants.
|
||
|
||
2. Insertion into a hierarchy means insertion into the table named in
|
||
the INSERT statement; updating or deletion affects whichever table(s)
|
||
the affected rows are found in. Updating cannot move a row from one
|
||
table to another.
|
||
|
||
3. Inheritance of a table implies inheriting all its constraints unless
|
||
ONLY is used or the constraints are subsequently dropped; again, dropping
|
||
operates through all descendant tables. A primary key, foreign key or
|
||
unique constraint cannot be dropped or modified for a descendant. A
|
||
unique index on a column is shared by all tables below the table for
|
||
which it is declared. It cannot be dropped for any descendant.
|
||
|
||
In other words, only NOT NULL and CHECK constraints can be dropped in
|
||
descendants.
|
||
|
||
In multiple inheritance, a column may inherit multiple unique indices
|
||
from its several ancestors. All inherited constraints must be satisfied
|
||
together (though check constraints may be dropped).
|
||
|
||
4. RI to a table implies the inclusion of all its descendants in the
|
||
check. Since a referenced column may be uniquely indexed further up
|
||
the hierarchy than in the table named, the check must ensure that
|
||
the referenced value occurs in the right segment of the hierarchy. RI
|
||
to one particular level of the hierarchy, excluding descendants, requires
|
||
the use of ONLY in the constraint.
|
||
|
||
5. Dropping a table implies dropping all its descendants.
|
||
|
||
6. Changes of permissions on a table propagate to all its descendants.
|
||
Permissions on descendants may be looser than those on ancestors; they
|
||
may not be more restrictive.
|
||
|
||
|
||
This scheme is a lot more restrictive than C++'s or Eiffel's definition
|
||
of inheritance, but it seems to me to make the concept truly useful,
|
||
without introducing excessive complexity.
|
||
|
||
============================================================
|
||
|
||
--
|
||
Oliver Elphick Oliver.Elphick@lfix.co.uk
|
||
Isle of Wight http://www.lfix.co.uk/oliver
|
||
PGP: 1024R/32B8FAA1: 97 EA 1D 47 72 3F 28 47 6B 7E 39 CC 56 E4 C1 47
|
||
GPG: 1024D/3E1D0C1C: CA12 09E0 E8D5 8870 5839 932A 614D 4C34 3E1D 0C1C
|
||
========================================
|
||
"If anyone has material possessions and sees his
|
||
brother in need but has no pity on him, how can the
|
||
love of God be in him?"
|
||
I John 3:17
|
||
|
||
|
||
|
||
From pgsql-hackers-owner+M9621@postgresql.org Mon Jun 4 21:53:36 2001
|
||
Return-path: <pgsql-hackers-owner+M9621@postgresql.org>
|
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|
||
(envelope-from chriskl@familyhealth.com.au)
|
||
From: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
||
To: "Hackers" <pgsql-hackers@postgresql.org>
|
||
Subject: [HACKERS] Question about inheritance
|
||
Date: Tue, 5 Jun 2001 09:42:38 +0800
|
||
Message-ID: <ECEHIKNFIMMECLEBJFIGEENPCAAA.chriskl@familyhealth.com.au>
|
||
MIME-Version: 1.0
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|
||
Status: OR
|
||
|
||
Hi guys,
|
||
|
||
It's relatively straightforward to allow check constraints to be inherited -
|
||
but is it really possible to ever do the same with primary, unique or even
|
||
foreign constraints?
|
||
|
||
ie. Say a table has a primary key and I inherit from this table. Since the
|
||
primary key is an index on the parent table, I could just create another
|
||
index on the child table, on the same column.
|
||
|
||
However - because we are dealing with two separate indices, it should still
|
||
be possible to insert duplicate values into the parent table and the child
|
||
table shouldn't it? This means that when a query is run over the parent
|
||
table that includes results from the child table then you will get duplicate
|
||
results in a supposedly primary index.
|
||
|
||
Similar arguments seem to apply to unique and foreign constraints. If you
|
||
could use aggregate functions in check constraints - you'd have another
|
||
problem. And if asserts were ever implemented - same thing...
|
||
|
||
Am I misunderstanding how the mechanism works, or is this a big, not easily
|
||
solved, problem?
|
||
|
||
Chris
|
||
|
||
|
||
---------------------------(end of broadcast)---------------------------
|
||
TIP 6: Have you searched our list archives?
|
||
|
||
http://www.postgresql.org/search.mpl
|
||
|
||
From pgsql-hackers-owner+M9623@postgresql.org Mon Jun 4 22:17:50 2001
|
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Mon, 4 Jun 2001 22:07:42 -0400 (EDT)
|
||
To: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
||
cc: "Hackers" <pgsql-hackers@postgresql.org>
|
||
Subject: Re: [HACKERS] Question about inheritance
|
||
In-Reply-To: <ECEHIKNFIMMECLEBJFIGEENPCAAA.chriskl@familyhealth.com.au>
|
||
References: <ECEHIKNFIMMECLEBJFIGEENPCAAA.chriskl@familyhealth.com.au>
|
||
Comments: In-reply-to "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
||
message dated "Tue, 05 Jun 2001 09:42:38 +0800"
|
||
Date: Mon, 04 Jun 2001 22:07:42 -0400
|
||
Message-ID: <11249.991706862@sss.pgh.pa.us>
|
||
From: Tom Lane <tgl@sss.pgh.pa.us>
|
||
Precedence: bulk
|
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Sender: pgsql-hackers-owner@postgresql.org
|
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Status: OR
|
||
|
||
"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
|
||
> Am I misunderstanding how the mechanism works, or is this a big, not easily
|
||
> solved, problem?
|
||
|
||
The latter. Check the list archives for previous debates about this.
|
||
It's not real clear whether an inherited primary key should be expected
|
||
to be unique across the whole inheritance tree, or only unique per-table
|
||
(IIRC, plausible examples have been advanced for each case). If we want
|
||
uniqueness across multiple tables, it'll take considerable work to
|
||
create an index mechanism that'd enforce it.
|
||
|
||
regards, tom lane
|
||
|
||
---------------------------(end of broadcast)---------------------------
|
||
TIP 5: Have you checked our extensive FAQ?
|
||
|
||
http://www.postgresql.org/users-lounge/docs/faq.html
|
||
|
||
From pgsql-hackers-owner+M9664@postgresql.org Tue Jun 5 17:56:17 2001
|
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Return-path: <pgsql-hackers-owner+M9664@postgresql.org>
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Date: Tue, 5 Jun 2001 13:08:58 +1000
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Subject: Re: [HACKERS] Question about inheritance
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||
|
||
|
||
|
||
>It's relatively straightforward to allow check constraints to be inherited -
|
||
>but is it really possible to ever do the same with primary, unique or even
|
||
>foreign constraints?
|
||
|
||
You would either have to check each index in the hierarchy or else have
|
||
a single index across the whole hierarchy and check that. Obviously the
|
||
latter would be generally more useful.
|
||
|
||
As with all things inheritance, it is usually the right thing, and a good
|
||
default that things be inherited. So ideally, indexes should work across
|
||
whole hierarchies as well as primary, unique and foreign constraints.
|
||
It could be argued that not inheriting is of very limited usefulness.
|
||
|
||
|
||
|
||
|
||
---------------------------(end of broadcast)---------------------------
|
||
TIP 4: Don't 'kill -9' the postmaster
|
||
|
||
From pgsql-hackers-owner+M9627@postgresql.org Mon Jun 4 23:58:36 2001
|
||
Return-path: <pgsql-hackers-owner+M9627@postgresql.org>
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||
Received: from postgresql.org (webmail.postgresql.org [216.126.85.28])
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||
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|
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Date: Mon, 4 Jun 2001 20:46:34 -0700 (PDT)
|
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From: Stephan Szabo <sszabo@megazone23.bigpanda.com>
|
||
To: Christopher Kings-Lynne <chriskl@familyhealth.com.au>
|
||
cc: Hackers <pgsql-hackers@postgresql.org>
|
||
Subject: Re: [HACKERS] Question about inheritance
|
||
In-Reply-To: <ECEHIKNFIMMECLEBJFIGEENPCAAA.chriskl@familyhealth.com.au>
|
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Message-ID: <Pine.BSF.4.21.0106042039040.7433-100000@megazone23.bigpanda.com>
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|
||
Status: OR
|
||
|
||
On Tue, 5 Jun 2001, Christopher Kings-Lynne wrote:
|
||
|
||
> Hi guys,
|
||
>
|
||
> It's relatively straightforward to allow check constraints to be inherited -
|
||
> but is it really possible to ever do the same with primary, unique or even
|
||
> foreign constraints?
|
||
>
|
||
> ie. Say a table has a primary key and I inherit from this table. Since the
|
||
> primary key is an index on the parent table, I could just create another
|
||
> index on the child table, on the same column.
|
||
>
|
||
> However - because we are dealing with two separate indices, it should still
|
||
> be possible to insert duplicate values into the parent table and the child
|
||
> table shouldn't it? This means that when a query is run over the parent
|
||
> table that includes results from the child table then you will get duplicate
|
||
> results in a supposedly primary index.
|
||
>
|
||
> Similar arguments seem to apply to unique and foreign constraints. If you
|
||
> could use aggregate functions in check constraints - you'd have another
|
||
> problem. And if asserts were ever implemented - same thing...
|
||
>
|
||
> Am I misunderstanding how the mechanism works, or is this a big, not easily
|
||
> solved, problem?
|
||
|
||
It's a big deal. Actually check constraints have a similar problem if you
|
||
allow inherited constraints to be dropped. "Why does 'select * from
|
||
base;' give me rows where value<10 since there's a check value>=10
|
||
on the table?"
|
||
|
||
As Tom said, the unique constraint thing is still questionable which is
|
||
the more meaningful semantics. If we ever want to allow foreign key
|
||
constraints to inheritance trees, we need *some* way to guarantees
|
||
uniqueness across the tree even if that isn't through the unique
|
||
constraint.
|
||
|
||
|
||
---------------------------(end of broadcast)---------------------------
|
||
TIP 6: Have you searched our list archives?
|
||
|
||
http://www.postgresql.org/search.mpl
|
||
|
||
From pgsql-hackers-owner+M9638@postgresql.org Tue Jun 5 06:30:37 2001
|
||
Return-path: <pgsql-hackers-owner+M9638@postgresql.org>
|
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|
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|
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To: <pgsql-hackers@postgresql.org>
|
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Subject: Re: [HACKERS] Question about inheritance
|
||
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Status: OR
|
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|
||
> "Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
|
||
> > Am I misunderstanding how the mechanism works, or is this a big, not
|
||
easily
|
||
> > solved, problem?
|
||
>
|
||
> The latter. Check the list archives for previous debates about this.
|
||
> It's not real clear whether an inherited primary key should be expected
|
||
> to be unique across the whole inheritance tree, or only unique per-table
|
||
> (IIRC, plausible examples have been advanced for each case). If we want
|
||
> uniqueness across multiple tables, it'll take considerable work to
|
||
> create an index mechanism that'd enforce it.
|
||
>
|
||
IMHO current behaviour of PostgreSQL with inherited PK, FK, UNIQUE is
|
||
simply
|
||
bug not only from object-oriented but even object-related point of view.
|
||
Now
|
||
I can violate parent PK by inserting duplicate key in child!
|
||
|
||
Inherited tables should honours all constraints from parent. If I change
|
||
some constraint (seems only FK, but not PK or UNIQUE) I should be able to
|
||
do
|
||
it in more restrictive manner. For example, two base table is connected via
|
||
FK. I can change such FK in childs from base1->base2 to child1->child2 (or
|
||
child3) but not to child1->not_inherited_from_base2. CHECK, DEFAULT, NOT
|
||
NULL are more free to changes, isn't it?
|
||
|
||
IMHO last message in doc/TODO.details/inheritance from Oliver Elphick is a
|
||
good direction for implementing with exception on more rectrictive child FK
|
||
constraint (p.3 of message).
|
||
|
||
As for me, I was pushed to rollback to scheme with no inheritance at all in
|
||
my project for now. So I'm very interesting in implementing of right
|
||
inheritance and I wanted to ask similar question in one of the lists in
|
||
near
|
||
future.
|
||
|
||
Regards,
|
||
Dmitry
|
||
|
||
|
||
|
||
|
||
---------------------------(end of broadcast)---------------------------
|
||
TIP 6: Have you searched our list archives?
|
||
|
||
http://www.postgresql.org/search.mpl
|
||
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