Re: ENABLE/DISABLE CONSTRAINT NAME

From: Bernd Helmle <mailings(at)oopsware(dot)de>
To: Robert Haas <robertmhaas(at)gmail(dot)com>, wangshuo(at)highgo(dot)com(dot)cn
Cc: Peter Eisentraut <peter_e(at)gmx(dot)net>, David Johnston <polobo(at)yahoo(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>, Jeff Davis <pgsql(at)j-davis(dot)com>
Subject: Re: ENABLE/DISABLE CONSTRAINT NAME
Date: 2013-09-24 09:58:25
Message-ID: BB11006AFB4CF43C55C89345@apophis.credativ.lan
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--On 13. September 2013 20:17:19 -0400 Robert Haas <robertmhaas(at)gmail(dot)com>
wrote:

> You're missing the point. Peter wasn't worried that your patch throws
> an error; he's concerned about the fact that it doesn't.
>
> In PostgreSQL, you can only create the following view because test1
> has a primary key over column a:
>
> => create table test1 (a int constraint pk primary key, b text);
> => create view test2 as select a, b from test1 group by a;
> => alter table test1 drop constraint pk;
>
> The reason that, if the primary key weren't there, it would be
> ambiguous which row should be returned as among multiple values where
> a is equal and b is not. If you can disable the constraint, then you
> can create precisely that problem.

Hmm not sure i understand this argument either: this patch doesn't allow
disabling a primary key. It only supports FKs and CHECK constraints
explicitly.

--
Thanks

Bernd

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