Re: Not null contraints

At 02:02 14/10/00 -0400, Tom Lane wrote:
>Philip Warner <pjw(at)rhyme(dot)com(dot)au> writes:
>> At 00:26 14/10/00 -0400, Tom Lane wrote:
>>>> I tried updating pg_attribute & setting attnotnull to 'f' for the
field in
>>>> question. This seems to have worked. Is it safe?! - is there anything
>>>> else I should be aware of?
>>>
>>> Yup, that should do the trick. Not much magic here...
>
>> Just to confirm - does this mean we have ALTER TABLE ADD CONSTRAINT, but
>> not ALTER TABLE DROP CONSTRAINT. If so, should it go on a list somewhere?
>
>No, it just means that NOT NULL constraint is handled via a special
>flag attached to the column's pg_attribute entry.

So there is no 'ALTER TABLE ALTER <field> ALLOW NULLS' or whatever.

>Another relevant comment is that *removing* a NOT NULL constraint
>doesn't pose any risk of creating invalid entries in the table data.
>So there's no need to worry about cross-checking.

This should apply to removing *any* constraint AFAICT...

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