Add schema mention.
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Bruce Momjian
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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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cc: Tom Lane <tgl@sss.pgh.pa.us>
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References: <200105220437.f4M4bUA00539@candle.pha.pa.us>
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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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event_id INTEGER REFERENCES WEBCAL.tasks(event_id) ON DELETE CASCADE,
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user_id VARCHAR2(25) REFERENCES SERVICES.users(user_id) ON DELETE CASCADE,
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confirmed CHAR(1),
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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 A.SAMPLE_ID,
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A.CONCENTRATION,
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A.CASNO,
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B.PARAMETER,
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C.DESCRIPTION AS STYPE
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FROM HAI.RESULTS A, SAMPLETRACK.PARAMETERS B,
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SAMPLETRACK.SAMPLE_TYPE C
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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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