| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Greg Stark <gsstark(at)mit(dot)edu> |
| Cc: | Martijn van Oosterhout <kleptog(at)svana(dot)org>, Hannu Krosing <hannu(at)skype(dot)net>, Simon Riggs <simon(at)2ndquadrant(dot)com>, "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: effective SELECT from child tables |
| Date: | 2005-10-03 03:00:21 |
| Message-ID: | 12346.1128308421@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Greg Stark <gsstark(at)mit(dot)edu> writes:
> It would be nice to be able to do:
> ALTER TABLE ADD foo integer DEFAULT 1
> And there's no question of what what the semantics of this are.
Sure, but you can only optimize this if the default expression is
immutable...
> On the other hand if you do
> ALTER TABLE ADD foo integer
> and then later do
> ALTER TABLE ALTER foo SET DEFAULT 1
> then there is a window where all those foos are NULL and then they magically
> become 1? That doesn't seem tenable.
It'd also be contrary to the SQL spec, AFAICS.
Here's another interesting case to think about:
ALTER TABLE ADD foo integer DEFAULT 1
...
ALTER TABLE ALTER foo SET DEFAULT 2
You'll have to pay the table-traversal cost on one step or the other.
regards, tom lane
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