Re: Not null contraints

At 02:02 14/10/00 -0400, Tom Lane wrote:
>Philip Warner <pjw@rhyme.com.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...

----------------------------------------------------------------
Philip Warner                    |     __---_____
Albatross Consulting Pty. Ltd.   |----/       -  \
(A.B.N. 75 008 659 498)          |          /(@)   ______---_
Tel: (+61) 0500 83 82 81         |                 _________  \
Fax: (+61) 0500 83 82 82         |                 ___________ |
Http://www.rhyme.com.au          |                /           \|
                                 |    --________--
PGP key available upon request,  |  /
and from pgp5.ai.mit.edu:11371   |/