Re: altering a column's collation leaves an invalid foreign key

On Fri, Apr 12, 2024 at 5:06 PM jian he <jian.universality@gmail.com> wrote:
>
> On Tue, Mar 26, 2024 at 1:00 PM jian he <jian.universality@gmail.com> wrote:
> >
> > On Mon, Mar 25, 2024 at 2:47 PM Paul Jungwirth
> > <pj@illuminatedcomputing.com> wrote:
> > >
> > > On 3/23/24 10:04, Paul Jungwirth wrote:
> > > > Perhaps if the previous collation was nondeterministic we should force a re-check.
> > >
> > > Here is a patch implementing this. It was a bit more fuss than I expected, so maybe someone has a
> > > better way.
I think I found a simple way.

the logic is:
* ATExecAlterColumnType changes one column once at a time.
* one column can only have one collation. so we don't need  to store a
list of collation oid.
* ATExecAlterColumnType we can get the new collation (targetcollid)
and original collation info.
* RememberAllDependentForRebuilding  will check the column dependent,
whether this column is referenced by a foreign key or not information
is recorded.
so AlteredTableInfo->changedConstraintOids have the primary key and
foreign key oids.
* ATRewriteCatalogs will call ATPostAlterTypeCleanup (see the comments
in ATRewriteCatalogs)
* for tab->changedConstraintOids (foreign key, primary key) will call
ATPostAlterTypeParse, so
for foreign key (con->contype == CONSTR_FOREIGN)  will call TryReuseForeignKey.
* in TryReuseForeignKey, we can pass the information that our primary
key old collation is nondeterministic
and old collation != new collation to the foreign key constraint.
so foreign key can act accordingly at ATAddForeignKeyConstraint (old_check_ok).


based on the above logic, I add one bool in struct AlteredTableInfo,
one bool in struct Constraint.
bool in AlteredTableInfo is for storing it, later passing it to struct
Constraint.
we need bool in Constraint because ATAddForeignKeyConstraint needs it.