On 01/14/2016 12:59 AM, Karsten Hilbert wrote:
On Wed, Jan 13, 2016 at 12:10:15PM -0800, Adrian Klaver wrote:
On 01/13/2016 11:38 AM, Karsten Hilbert wrote:
create table parent (
not_null_in_parent integer not null
);
create table child() inherits (parent);
alter table child
alter column not_null_in_parent
drop not null
;
Is this a bug or am I doing things I shouldn't hope work ?
The latter if I am following the below correctly:
http://www.postgresql.org/docs/9.5/static/ddl-inherit.html
"All check constraints and not-null constraints on a parent table are
automatically inherited by its children. Other types of constraints (unique,
primary key, and foreign key constraints) are not inherited."
Hello Adrian, thanks for chipping in. I am aware of the above
paragraph. In fact, it made me choose the inheritance
approach to the problem at hand in the first place :-)
Note though that, usually, inheriting is a one-time act --
such as during child table creation. What stays behind is the
legacy - which can be changed (DROP NOT NULL).
I was, then, surprised by the fact that the pg_dump /
pg_restore cycle did not "faithfully" reproduce the child
table. That made me question my ways.
Maybe I shouldn't have been surprised because PG inheritance
doesn't end at table creation time (child and parent are
still linked through data even in the future).
Actually more than that:
http://www.postgresql.org/docs/9.4/interactive/sql-createtable.html
INHERITS ( parent_table [, ... ] )
Use of INHERITS creates a persistent relationship between the new child
table and its parent table(s). Schema modifications to the parent(s)
normally propagate to children as well, and by default the data of the
child table is included in scans of the parent(s).
Meatspace inheritance is more like
CREATE TABLE pseudo_child_table AS SELECT FROM pseudo_parent_table ...
While PG inheritance is a bit more like view-on-steroids.
Thanks,
Karsten
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
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