From: Hannu Krosing <hannu@trust.ee>
To: Rusty Brooks <rbrooks@utdallas.edu>
Cc: Tatsuo Ishii <t-ishii@sra.co.jp>
Cc: Thomas Lockhart <lockhart@alumni.caltech.edu>
Cc: robertC@opmr.com
Cc: pgsql-interfaces@postgreSQL.org
Subject: Re: [INTERFACES] How do I drop a column from a table?
Date: Tue, 31 Aug 1999 22:06:25 +0300
Message-ID: <37CC27B1.D88C7CEA@trust.ee> (raw)
References: <Pine.LNX.4.10.9908310935550.8672-100000@pickles>
Rusty Brooks wrote:
>
> On Tue, 31 Aug 1999, Tatsuo Ishii wrote:
>
> ==>But this method might lose some characteristics such as primary key,
> ==>unique constraints, no?
>
> I'm not sure, but if it does you can add them back with unique indexes. I
> also think you can add these attributes back with an alter table combined
> with a CONTSTRAINT x PRIMARYKEY(col)
AFAIK PostgreSQL dos not support most of the ALTER TABLE functionality,
only ADD COLUMN and RENAME COLUMN and RENAME are supported ;(
ALTERing, ADDing and DROPping of constraints is not supported, as is not
disbling indexes. There is a workaround for UNIQUE constraint, which is
implemented using UNIQUE INDEXes anyway and thus can be manipulated by
DROP/CREATE index, but you can't change the NULL/NOT NULL constraint,
at least without directly manipulating system tables.
Also any changing of types is not allowed (Oracle allows type changes of
INT -> FLOAT, NUMERIC->CHAR and of shorter (VAR)CHAR types to longer
ones)
Btw, UNIQUE constraint is implemented in a way that does not allow
duplicates
even inside transactions:
hannu=> create table uni(
hannu-> i int primary key
hannu-> );
NOTICE: CREATE TABLE/PRIMARY KEY will create implicit index uni_pkey
for table uni
CREATE
hannu=> insert into uni values(1);
INSERT 2517548 1
hannu=> insert into uni values(2);
INSERT 2517549 1
hannu=> update uni set i=i+1;
ERROR: Cannot insert a duplicate key into a unique index
I think this is the same type of flaw that discouraged Vadim from
implementing FOREIGN KEYs based on the code from contrib/
So there is a long way to go to acieve more or less dynamic table
manipulation;
currently table defs are mostly write-only.
-----
Hannu
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To: pgsql-interfaces@postgresql.org
Cc: hannu@trust.ee, rbrooks@utdallas.edu, t-ishii@sra.co.jp, lockhart@alumni.caltech.edu, robertC@opmr.com
Subject: Re: [INTERFACES] How do I drop a column from a table?
In-Reply-To: <37CC27B1.D88C7CEA@trust.ee>
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