public inbox for [email protected]  

help / color / mirror / Atom feed

From: Achilleus Mantzios <[email protected]>
To: Erik Thiele <[email protected]>
Cc: Bruno Wolff III <[email protected]>
Cc: [email protected]
Subject: Re: special integrity constraints
Date: Tue, 23 Mar 2004 09:26:29 +0200 (EET)
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

O kyrios Erik Thiele egrapse stis Mar 22, 2004 :

Could it be possible to convert *any* CHECK
constraint problem into an equivalent
DEFERRABLE FK constraint problem?

That is for *every* CHECK CONSTRAINT cc
create (and maintain) 2 additional 1 row tables (cc1(val),cc2(val)) in 
such a way
that cc is met if and only if (cc1.val = cc2.val).

Its kinda awkard, and i think that if your situation
is (gets) any more complicated tou should delegate that task
to the application.

The whole idea was for you too prove that using only supported pgsql
features, you can achieve the equivalent effect of deferrable
check constraints.

> On Mon, 22 Mar 2004 09:12:11 -0600
> Bruno Wolff III <[email protected]> wrote:
> 
> > On Mon, Mar 22, 2004 at 14:10:42 +0100,
> >   Erik Thiele <[email protected]> wrote:
> > > 
> > > it means (((count_rows(a)+count_rows(b)) modulo 2) == 0)
> > 
> > OK, that means my FK suggestion won't help. The other suggestion about
> > putting triggers on "a" and "b" to update a count in another table
> > that has a deferred check constraint on it may be your best bet.
> > This will be a source of contention, but that may or may not be all
> > that important depending on how often you are updating "a" and "b".
> > 
> 
> there is no such thing as a deferred check constraint:
> 
> DEFERRABLE
> NOT DEFERRABLE
> 
> This controls whether the constraint can be deferred. A constraint that
> is not deferrable will be checked immediately after every command.
> Checking of constraints that are deferrable may be postponed until the
> end of the transaction (using the SET CONSTRAINTS command). NOT
> DEFERRABLE is the default. 
> 
> !!! Only foreign key constraints currently accept
> this clause. All other constraint types are not deferrable. !!!
> 
> 
> cu
> erik
> 
> 

-- 
-Achilleus

view thread (13+ messages)

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected]
  Subject: Re: special integrity constraints
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox