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In-Reply-To: <69f0a887-a4ed-49cf-9d63-923891006658@illuminatedcomputing.com>
From: jian he <jian.universality@gmail.com>
Date: Tue, 26 Mar 2024 13:00:00 +0800
Message-ID: <CACJufxE8BePAtzoedMo5Fyznif_6vWy0-aq7WjaDd09nd6k4YQ@mail.gmail.com>
Subject: Re: altering a column's collation leaves an invalid foreign key
To: Paul Jungwirth <pj@illuminatedcomputing.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Mon, Mar 25, 2024 at 2:47=E2=80=AFPM 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.
>

+ /* test follows the one in ri_FetchConstraintInfo() */
+ if (ARR_NDIM(arr) !=3D 1 ||
+ ARR_HASNULL(arr) ||
+ ARR_ELEMTYPE(arr) !=3D INT2OID)
+ elog(ERROR, "conkey is not a 1-D smallint array");
+ attarr =3D (AttrNumber *) ARR_DATA_PTR(arr);
+
+ /* stash a List of the collation Oids in our Constraint node */
+ for (i =3D 0; i < numkeys; i++)
+ con->old_collations =3D lappend_oid(con->old_collations,
+  list_nth_oid(changedCollationOids, attarr[i] - 1));

I don't understand the "ri_FetchConstraintInfo" comment.


+static void
+RememberCollationForRebuilding(AttrNumber attnum, AlteredTableInfo *tab)
+{
+ Oid typid;
+ int32 typmod;
+ Oid collid;
+ ListCell   *lc;
+
+ /* Fill in the list with InvalidOid if this is our first visit */
+ if (tab->changedCollationOids =3D=3D NIL)
+ {
+ int len =3D RelationGetNumberOfAttributes(tab->rel);
+ int i;
+
+ for (i =3D 0; i < len; i++)
+ tab->changedCollationOids =3D lappend_oid(tab->changedCollationOids,
+ InvalidOid);
+ }
+
+ get_atttypetypmodcoll(RelationGetRelid(tab->rel), attnum,
+  &typid, &typmod, &collid);
+
+ lc =3D list_nth_cell(tab->changedCollationOids, attnum - 1);
+ lfirst_oid(lc) =3D collid;
+}

do we need to check if `collid` is a valid collation?
like:

if (!OidIsValid(collid))
{
lc =3D list_nth_cell(tab->changedCollationOids, attnum - 1);
lfirst_oid(lc) =3D collid;
}