From: | Hannu Krosing <hannu(at)tm(dot)ee> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Don Baccus <dhogaza(at)pacifier(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Hiroshi Inoue <Inoue(at)tpf(dot)co(dot)jp>, PostgreSQL Development <pgsql-hackers(at)postgreSQL(dot)org> |
Subject: | Re: Happy column adding (was RE: [HACKERS] Happy column dropping) |
Date: | 2000-01-26 00:31:34 |
Message-ID: | 388E4066.3CDEE504@tm.ee |
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Lists: | pgsql-hackers |
Tom Lane wrote:
>
> Don Baccus <dhogaza(at)pacifier(dot)com> writes:
> > However, heap_getattr still won't see the default since it simply
> > checks to see of the attribute number falls off the end of the
> > tuple and then returns null.
>
> Right.
>
> > There's no provision for then pulling out the default value and
> > returning it instead.
>
> Would it even be possible to do that? I'm not sure that heap_getattr
> has any way to find the default. It only has a TupleDesc, not a
> reference to the relation itself...
but could it not return a special value, say COLUMN_DEFAULT, that upper
levels know to replace with the real default. Of course it get's funny if
if the default is nextval('myseq') or CURRENT_TIME.
another way to approach the whole problem is to have something like
generation_id in each tuple that tells which version of TupleDesc applies
to this tuple, but it seems to complicate things even further.
-----------------
Hannu
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