Re: ATTACH PARTITION seems to ignore column generation status

I wrote:
> After thinking about this awhile, I feel that we ought to disallow
> it in the traditional-inheritance case as well. The reason is that
> there are semantic prohibitions on inserting or updating a generated
> column, eg

> regression=# create table t (f1 int, f2 int generated always as (f1+1) stored);
> CREATE TABLE
> regression=# update t set f2=42;
> ERROR: column "f2" can only be updated to DEFAULT
> DETAIL: Column "f2" is a generated column.

> It's not very reasonable to have to recheck that for child tables,
> and we don't. But if one does this:

> regression=# create table pp (f1 int, f2 int);
> CREATE TABLE
> regression=# create table cc (f1 int, f2 int generated always as (f1+1) stored) inherits(pp);
> NOTICE: merging column "f1" with inherited definition
> NOTICE: merging column "f2" with inherited definition
> CREATE TABLE
> regression=# insert into cc values(1);
> INSERT 0 1
> regression=# update pp set f2 = 99 where f1 = 1;
> UPDATE 1
> regression=# table cc;
> f1 | f2
> ----+----
> 1 | 99
> (1 row)

> That is surely just as broken as the partition-based case.

So what we need is about like this. This is definitely not something
to back-patch, since it's taking away what had been a documented
behavior. You could imagine trying to prevent such UPDATEs instead,
but I judge it not worth the trouble. If anyone were actually using
this capability we'd have heard bug reports.

regards, tom lane