And yeah, certainly there's a bug as you point out.
postgres=# create table a1 (ff1 int, constraint chk check (ff1 > 0));
postgres=# create table b1 (ff1 int);
postgres=# alter table only b1 add constraint chk check (ff1 > 0);
postgres=# alter table b1 inherit a1;
The last command should have refused to inherit.
Regards,
Nikhils
On Fri, Dec 23, 2011 at 8:55 AM, Nikhil Sontakke
<nikkhils@gmail.com> wrote:
Hi,
There is at least one other
problem. Consider:
rhaas=# create table a (ff1 int, constraint chk check (ff1 > 0));
CREATE TABLE
rhaas=# create table b (ff1 int, constraint chk check (ff1 > 0));
CREATE TABLE
rhaas=# alter table b inherit a;
ALTER TABLE
This needs to fail if chk is an "only" constraint, but it doesn't,
even with this patch.
As you rightly point out, this is because we cannot specify ONLY constraints inside a CREATE TABLE as of now.
I think that part of the problem here is fuzzy thinking about the
meaning of the word "ONLY" in "ALTER TABLE ONLY b". The word "ONLY"
there is really supposed to mean that the operation is performed on b
but not on its descendents; but that's not what you're doing: you're
really performing a different operation. In theory, for a table with
no current descendents, ALTER TABLE ONLY b and ALTER TABLE b ought to
be identical, but here they are not. I think that's probably bad.
ONLY has inheritance based connotations for present/future children. ALTER ONLY combined with ADD is honored better now with this patch IMO (atleast for constraints I think).
Another manifestation of this problem is that there's no way to add an
ONLY constraint in a CREATE TABLE command. I think that's bad, too:
it should be possible to declare any constraint at table creation
time, and if the ONLY were part of the constraint definition rather
than part of the target-table specification, that would work fine. As
it is, it doesn't.
I am tempted to say we should revert this and rethink. I don't
believe we are only a small patch away from finding all the bugs here.
Sure, if we all think that CREATE TABLE should support ONLY CONSTRAINT type of syntax, then +1 for reverting this and a subsequent revised submission.
Regards,
Nikhils