Обсуждение: UPDATE with invalid domain constraint

hi.

should UPDATE statement need to verify that the domain value is satisfied with
invalid domain constraints?
Álvaro Herrera already mentioned this in [1], but I just want to confirm it.

drop table if exists dt1;
drop domain if exists d1;
create domain d1 as int;
create table dt1(i int, c d1);
insert into dt1 values(1,2);
alter domain d1 add constraint cc check(value <> 2) not valid;

update dt1 set i = i + 1;
update dt1 set c = c;
update dt1 set i = i + 1, c = c;
update dt1 set i = i + 1, c = c::d1;

Should the four statements above result in an error?
This only happens with UPDATE, since INSERT will check with domain
invalid constraints.

this ``update dt1 set i = i + 1, c = 2;``
do return error, which is expected.

[1]: https://postgr.es/m/202508140957.4daktvyr7xiw@alvherre.pgsql

On Tue, Aug 19, 2025 at 10:08 PM jian he <jian.universality@gmail.com> wrote:
>

> drop table if exists dt1;
> drop domain if exists d1;
> create domain d1 as int;
> create table dt1(i int, c d1);
> insert into dt1 values(1,2);
> alter domain d1 add constraint cc check(value <> 2) not valid;
>

> update dt1 set i = i + 1;
> update dt1 set c = c;
> update dt1 set i = i + 1, c = c;
> update dt1 set i = i + 1, c = c::d1;
>
> Should the four statements above result in an error?
> This only happens with UPDATE, since INSERT will check with domain
> invalid constraints.

the main idea is that
if we find out that a Var Node type is domain with invalid constraint
then we convert the
Var to CoerceToDomain node.


explain (verbose, costs off) update dt1 set i = i + 1;
            QUERY PLAN
----------------------------------
 Update on public.dt1
   ->  Seq Scan on public.dt1
         Output: (i + 1), c, ctid
(3 rows)

as you can see from the "Output:", column "c" is also here,
In rewriteTargetListIU, In rewriteTargetListIU, I use makeTargetEntry to produce
a new TargetEntry for column c, set its expr to a CoerceToDomain node, and set
resjunk to true.