182 lines
8.3 KiB
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182 lines
8.3 KiB
Plaintext
From ronz@ravensfield.com Tue May 22 17:35:37 2001
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From: Andrew Rawnsley <ronz@ravensfield.com>
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Organization: Ravensfield Geographic
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To: Bruce Momjian <pgman@candle.pha.pa.us>
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Subject: Re: [GENERAL] Queries across multiple databases (was: SELECT from a table in another database).
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Date: Tue, 22 May 2001 17:37:25 -0400
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X-Mailer: KMail [version 1.2]
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cc: Tom Lane <tgl@sss.pgh.pa.us>
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References: <200105220437.f4M4bUA00539@candle.pha.pa.us>
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Message-ID: <01052217372504.01367@coho.ravensfield.com>
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Status: ORr
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On Tuesday 22 May 2001 12:37am, Bruce Momjian wrote:
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> Can you send me a little sample of SCHEMA use?
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Pardon if this is more long-winded or tangental than you are looking for...
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What may beconfusing many people (not excluding myself from time to time) is
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that cross-schema queries may have nothing to do with cross-database queries,
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which is an entirely different kettle of trout.... SCHEMAs as used by at
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least by Oracle and Sybase are nothing more than users/object owners (I have
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no experience with DB2 or Informix, or anything more exotic than that).
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Just off the top of my head, what would satisfy most people would be to be
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able to refer to objects as OWNER.OBJECT, with owner being 'within' the
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database (i.e. DATABASE.OWNER.OBJECT, which is how Sybase does it. Oracle has
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no 'database' parallel like that). Whether you do it Oracle-fashion and use
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the term SCHEMA for owner pretty universally or Sybase fashion and just pay
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lip service to the word doesn't really matter (unless there is a standards
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compliance issue).
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As to creating schemas...In Oracle you have to execute the CREATE SCHEMA
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AUTHORIZATION <user> while logged in as that user before you can add objects
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under that user's ownership. While it seems trivial, if you have a situation
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where you do not want to grant a user session rights, you have to grant them
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session rights, log in as them, execute CREATE SCHEMA..., then revoke the
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session rights. Bah. A table created by user X in schema Y is also owned by
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user Y, and its user Y that has to have many of the object rights to create
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that table.
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In Sybase, its essentially the same except the only real use for the CREATE
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SCHEMA command is for compliance and to group some DDL commands together.
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Other than that, Sybase always refers to schemas as owners. You don't have to
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execute CREATE SCHEMA... to create objects - you just need the rights. I've
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never used it at least - the only thing I see in it is eliminating the need
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to type 'go' after every DDL command.
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As for examples from Oracle space -
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Here is a foreign key reference with delete triggers from a table in
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schema/user PROJECT to tables in schemas/users SERVICES and WEBCAL:
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CREATE TABLE PROJECT.tasks_users (
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<EFBFBD> <20>event_id INTEGER REFERENCES WEBCAL.tasks(event_id) ON DELETE CASCADE,
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<EFBFBD> <20>user_id VARCHAR2(25) REFERENCES SERVICES.users(user_id) ON DELETE CASCADE,
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<EFBFBD> <20>confirmed CHAR(1),
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<EFBFBD> <20>PRIMARY KEY (event_id,user_id)
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);
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A join between tables in would be
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SELECT <20> A.SAMPLE_ID,
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> A.CONCENTRATION,
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> A.CASNO,
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> B.PARAMETER,
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> C.DESCRIPTION AS STYPE
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> FROM HAI.RESULTS A, SAMPLETRACK.PARAMETERS B,
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SAMPLETRACK.SAMPLE_TYPE C
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<EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> <20><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD> WHERE A.CASNO = B.CASNO AND A.SAMPLE_TYPE = B.SAMPLE_TYPE
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In both Oracle and Sybase, all the objects are in the same 'database'
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(instance in Oracle), as I assume they would be in Postgres. There is I
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assume a name space issue - one should be able to create a FOO.BAR and a
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BAR.BAR in the same database.
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> I may be adding it to
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> 7.2 inside the same code that maps temp table names to real tables.
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>
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Excellent! I see light at the end of the tunnel (I will say the Postgres
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maintainers are among the most solidly competent around - one never has any
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real doubts about the system's progress).
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--
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Regards,
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Andrew Rawnsley
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Ravensfield Digital Resource Group, Ltd.
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(740) 587-0114
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www.ravensfield.com
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From reedstrm@rice.edu Wed May 23 10:59:42 2001
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Return-path: <reedstrm@rice.edu>
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id 152a41-0006E5-00
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for <pgman@candle.pha.pa.us>; Wed, 23 May 2001 09:56:41 -0500
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Date: Wed, 23 May 2001 09:56:41 -0500
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From: "Ross J. Reedstrom" <reedstrm@rice.edu>
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To: Bruce Momjian <pgman@candle.pha.pa.us>
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Subject: Re: [HACKERS] Re: [GENERAL] Re: [GENERAL] Queries across multiple databases ?(was: SELECT from a table in another database).
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Message-ID: <20010523095641.D23741@rice.edu>
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References: <004c01c0e214$ce6c4800$1001a8c0@archonet.com> <200105221131.f4MBVIc28574@candle.pha.pa.us>
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In-Reply-To: <200105221131.f4MBVIc28574@candle.pha.pa.us>; from pgman@candle.pha.pa.us on Tue, May 22, 2001 at 07:31:18AM -0400
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Status: ORr
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Bruce -
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Around the first of the year, I started playing around with a schema
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implementation. As you may recall, my first crack at changing file storage
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names about a year ago was motivated by the need to avoid collisions
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once schema were available.
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Anyway, now that Vadim has removed a lot of the internal dependence
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on relname for keeping track of relations, using the new relfinenode
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many places relname used to be used, it seems to me that adding a
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parallel schemaname to all the data structures that use relname isn't
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as cumbersome as Peter might think. I hadn't tackled the relcache yet:
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perhaps concatenating the schemaname and relname to use as the hash key
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is the way to go for that.
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Unfortunately, all that code is now 4 months old, and on my machine
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at home. I has started with the rangetable entries, because hacked the
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parser to allow 'SELECT * FROM schemaname.tablename' was easier than
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'select schemaname.tablename.fieldname FROM', since the dot function
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calling convention isn't allowed in the range list, while it is in the
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target list.
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I seem to recall tripping up on the query plan printer, of all things,
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before other, paying work pushed it aside. I'll see if I can update that
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code to the current tree, and send you something, if you'd like.
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Ross
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On Tue, May 22, 2001 at 07:31:18AM -0400, Bruce Momjian wrote:
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> > > I'm not sure whether it is quite the way to do it, but I'd have a better
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> > > time with things if I could span databases in a single request. Are
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> > > there theoretical problems with spanning databases in a single query? Is
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> > > it a feature of bad database design & implementation?
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> >
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> > I think the developers are planning full schema support for the relatively
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> > near future (possibly even 7.2, but check the archives and see what's been
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> > said). Although it looks easy to access a table from another database,
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> > things can rapidly become more complicated as you start having to deal with
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> > transactions, triggers, rules, constraints...
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>
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> Schema is on my radar screen for 7.2. I am waiting to do some research
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> in what needs to be done, but my initial idea is to use the system cache
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> to do namespace mapping, just like is done now for temp tables.
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>
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> --
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> Bruce Momjian | http://candle.pha.pa.us
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> pgman@candle.pha.pa.us | (610) 853-3000
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> + If your life is a hard drive, | 830 Blythe Avenue
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> + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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>
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> ---------------------------(end of broadcast)---------------------------
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> TIP 2: you can get off all lists at once with the unregister command
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> (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
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