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Re: SET NULL / SET NOT NULL

From: Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com>
To: Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,Zeugswetter Andreas SB SD <ZeugswetterA(at)spardat(dot)at>,Peter Eisentraut <peter_e(at)gmx(dot)net>,Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: SET NULL / SET NOT NULL
Date: 2002-03-26 05:59:06
Message-ID: 20020325214602.E47891-100000@megazone23.bigpanda.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Tue, 26 Mar 2002, Christopher Kings-Lynne wrote:

> > Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au> writes:
> > > I have throught of at least two problems with changing nullability.  The
> > > first is primary keys.  I have to prevent people setting a
> > column involved
> > > in a PK to null, right?
> >
> > Probably so.
>
> And foreign keys - foreign keys only have to reference UNIQUE, right?  The
> nullability isn't an issue?

That should be fine.

> Lastly - in a multicolumn primary key, does EVERY column in the key need to
> be NOT NULL?

Well, it looks like the primary key will not be satisfied if any of the
values are NULL.

In my SQL 92 draft, 11.7 Syntax Rules 3a says:
    If the <unique specification> specifies PRIMARY KEY, then let
    SC be the <search condition>:

                 UNIQUE ( SELECT UCL FROM TN )
                 AND
                 ( UCL ) IS NOT NULL




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