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Re: question for serial types with CHECK conditions

From: "Guido Barosio" <gbarosio(at)gmail(dot)com>
To: "Michael Glaesemann" <grzm(at)seespotcode(dot)net>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: question for serial types with CHECK conditions
Date: 2007-04-28 16:34:15
Message-ID: f7f6b4c70704280934pc356c59g7e4877c7291f25c1@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Thanks for your reply Michael.

   My point was to step on the asumption that the implicit "serial"
call for a type represents the fact that the sequence will start
allways in the same place, unless inmediatelly after your "create
table" you plan to modify that, which makes no sense when we go back
to what the CREATE SEQUENCE represents for the case.

   For what I saw, straight foward what I did is wrong, but the server
allowed me to proceed. So yes, my fault, but with a bit of help,
right?

   After all I am just being boggus on a silly point. The range of
potential DBA's which may come to this situation is pretty small for
further discussions :)

Best wishes,
g.-

On 4/28/07, Michael Glaesemann <grzm(at)seespotcode(dot)net> wrote:
>
> On Apr 28, 2007, at 10:30 , Guido Barosio wrote:
>
> >   Now, my question is: Shouldn't postgresql avoid the creation of the
> > table while a serial type contains a check condition?
>
> My question to you is why should it? "a" SERIAL is a shorthand for
> creating an INTEGER column "a",  a sequence ("a_seq") with a
> dependency, and DEFAULT nextval(a_seq). There may be a valid reason
> someone wants to put additional constraints on the column, and I'm
> not sure why the server should second guess the DBA in this case. If
> the CHECK constraint isn't what you want, then don't include it: and
> in this case the server helpfully gave you an error which let you
> know that the CHECK constraint was not doing what you expected.
>
> Also, the server doesn't have the smarts to look into the CHECK
> constraint and decide if it makes sense in your case. For example,
> perhaps you want to have CHECK (a > 0), which won't really do
> anything for a default sequence. However, if the sequence is changed,
> it may return negative integers, which you may not want, so in some
> cases, CHECK (a > 0) may be a valid constraint *in your case*.
>
> The crux of the issue is that there may be valid reasons to have a
> CHECK constraint on a INTEGER (SERIAL) column, and the server is not
> (and will probably never be) smart enough to know your particular
> business rules without you telling it specifically.
>
> Does this help clarify the situation?
>
> Michael Glaesemann
> grzm seespotcode net
>
>
>


-- 
Guido Barosio
-----------------------
http://www.globant.com
guido(dot)barosio(at)globant(dot)com

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