Skip site navigation (1) Skip section navigation (2)

Re: Re: Changing the default value of an inherited column

From: ncm(at)zembu(dot)com (Nathan Myers)
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: Changing the default value of an inherited column
Date: 2001-03-30 21:40:25
Message-ID: 20010330134025.G3797@store.zembu.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Mar 30, 2001 at 11:05:53PM +0200, Peter Eisentraut wrote:
> Tom Lane writes:
> 
> > 3. The new column will have a default value if any of the combined
> > column specifications have one.  The last-specified default (the one
> > in the explicitly given column list, or the rightmost parent table
> > that gives a default) will be used.
> 
> This seems pretty random.  It would be more reasonable if multiple
> (default) inheritance weren't allowed unless you explicitly specify a new
> default for the new column, but we don't have a syntax for this.

I agree, but I thought the original issue was that PG _does_ now have 
syntax for it.  Any conflict in default values should result in either 
a failure, or "no default".  Choosing a default randomly, or according 
to an arbitrary and complicated rule (same thing), is a source of bugs.

> > 4. All relevant constraints from all the column specifications will
> > be applied.  In particular, if any of the specifications includes NOT
> > NULL, the resulting column will be NOT NULL.  (But the current
> > implementation does not support inheritance of UNIQUE or PRIMARY KEY
> > constraints, and I do not have time to add that now.)
> 
> This is definitely a violation of that Liskov Substitution.  If a context
> expects a certain table and gets a more restricted table, it will
> certainly notice.

Not so.  The rule is that the base-table code only has to understand
the derived table.  The derived table need not be able to represent
all values possible in the base table. 

Nathan Myers
ncm(at)zembu(dot)com

In response to

Responses

pgsql-hackers by date

Next:From: Peter EisentrautDate: 2001-03-30 21:45:39
Subject: Re: [HACKERS] Re: [ADMIN] User administration tool
Previous:From: Nathan MyersDate: 2001-03-30 21:30:35
Subject: Re: Re: Changing the default value of an inherited column

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group