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Re: [COMMITTERS] pgsql: Disallow changing/dropping default expression

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [COMMITTERS] pgsql: Disallow changing/dropping default expression
Date: 2006-06-27 15:15:47
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Lists: pgsql-committerspgsql-hackers
Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Tom Lane wrote:
>> Wasn't this patch rejected?

> Anyway, what is your opinion on this?

I thought we'd rejected it.  I'm not sure that we'd completely agreed
what the best thing to do is, but what this patch actually does is to
silently remove the dependency link.  That is, after

	create table t1 (f1 serial);
	alter table t1 alter column f1 drop default;

t1_f1_seq is still there, but now completely unconnected to t1.
That doesn't seem to me to satisfy the principle of least surprise.
It's certainly not what the TODO item says (reject the DROP DEFAULT).
I think we were considering the alternative of having the DROP DEFAULT
remove the sequence, which probably could be implemented painlessly
with a change in the way we set up the dependency links to start with.

In any case I don't like this patch: int/bool confusion, use of elog
instead of ereport for a user-facing error message, failure to adhere to
style guidelines for that message, etc.  (Although seeing that the error
message is unreachable code, maybe that doesn't matter ;-))  Aside from
the poor coding style, the whole idea of reaching into pg_depend to
remove a single dependency strikes me as a brute-force solution to
a problem that should have a more elegant answer.

			regards, tom lane

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