Re: patch for check constraints using multiple inheritance

On Fri, Jul 30, 2010 at 10:23 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Fri, Jul 30, 2010 at 10:11 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> The original design idea was that coninhcount/conislocal would act
>>> exactly like attinhcount/attislocal do for multiply-inherited columns.
>>> Where did we fail to copy that logic?
>
>> We didn't.  That logic is broken, too.
>
> Uh, full stop there.  If you think that the multiply-inherited column
> logic is wrong, it's you that is mistaken --- or at least you're going
> to have to do a lot more than just assert that you don't like it.
> We spent a *lot* of time hashing that behavior out, back around 7.3.

Well, I'm glad you spent a lot of time hashing it out, but you've got
a bug.  :-)

Since the output in the previous email apparently wasn't sufficient
for you to understand what the problem is, here it is in more detail.
Initial setup:

DROP SCHEMA IF EXISTS test_inheritance CASCADE;
CREATE SCHEMA test_inheritance;
SET search_path TO test_inheritance;
CREATE TABLE level_0_parent (i int);
CREATE TABLE level_0_child (a text) INHERITS (level_0_parent);
CREATE TABLE level_1_parent() INHERITS (level_0_parent);
CREATE TABLE level_1_child() INHERITS (level_0_child, level_1_parent);
CREATE TABLE level_2_parent() INHERITS (level_1_parent);
CREATE TABLE level_2_child() INHERITS (level_1_child, level_2_parent);

Then:

rhaas=# \d level_2_child
Table "test_inheritance.level_2_child"Column |  Type   | Modifiers
--------+---------+-----------i      | integer |a      | text    |
Inherits: level_1_child,         level_2_parent

rhaas=# ALTER TABLE level_0_parent ADD COLUMN a_new_column integer;
NOTICE:  merging definition of column "a_new_column" for child "level_1_child"
NOTICE:  merging definition of column "a_new_column" for child "level_2_child"
NOTICE:  merging definition of column "a_new_column" for child "level_2_child"
ALTER TABLE
rhaas=# ALTER TABLE level_0_parent DROP COLUMN a_new_column;
ALTER TABLE
rhaas=# \d level_2_child
Table "test_inheritance.level_2_child"   Column    |  Type   | Modifiers
--------------+---------+-----------i            | integer |a            | text    |a_new_column | integer |
Inherits: level_1_child,         level_2_parent

Adding a column to the toplevel parent of the inheritance hierarchy
and then dropping it again shouldn't leave a leftover copy of the
column in the grandchild.

rhaas=# ALTER TABLE level_2_child DROP COLUMN a_new_column;
ERROR:  cannot drop inherited column "a_new_column"

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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