FAQ

On Fri, Aug 6, 2010 at 12:31 AM, Jon Erdman (aka StuckMojo) wrote:
Description:        Setting NOT NULL on inherited column turns to real
column in dump

I think the fix here is relatively simple: make NOT NULL on an inherited
column dump as an ALTER TABLE.

If you set NOT NULL on an inherited column in a child table, then drop the
column from the parent, it's gone from both and all is well.

However, if you dump and restore the db, then drop the parent column, the
inherited column remains in the child table. This is a result of the NOT
NULL dumping as a column create in the child, which I assume then shadows
the inherited column after restore.
That sucks. I have a feeling it's going to be hard to fix properly
without this patch:

https://commitfest.postgresql.org/action/patch_view?id=312

I don't think your proposed fix will work because the NOT NULL-ness
could be either inherited or not inherited. The column could even be
inherited from multiple parents, some of which have a NOT NULL
constraint and others of which do not. Consider:

create table top1 (a int not null);
create table top2 (a int);
create table bottom () inherits (top1, top2);
alter table bottom no inherit <something>;

If <something> = top1, then bottom.a should now allow nulls, but if
<something> = top2, then it should still be not null. Unfortunately,
we don't do enough bookkeeping right now to distinguish those cases.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise Postgres Company

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postedAug 6, '10 at 4:31a
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