BUG #15642: UPDATE statements that change a partition key and FDW partitions problem.

(2019/02/19 23:13), PG Bug reporting form wrote:

The following bug has been logged on the website:

Update statement which changes value of partition key doesn't doesn't work
with FDW partitions.

Test script:
\c postgres
drop database IF EXISTS test;
drop database IF EXISTS test0;
drop database IF EXISTS test1;
create database test;
create database test0;
create database test1;
\c test0
create table t (id integer not null, constraint id_check check (id<0));
\c test1
create table t (id integer not null, constraint id_check check (id>=0));
\c test
create extension postgres_fdw;
create server if not exists test0 FOREIGN DATA WRAPPER postgres_fdw OPTIONS
(dbname 'test0');
create server if not exists test1 FOREIGN DATA WRAPPER postgres_fdw OPTIONS
(dbname 'test1');
CREATE USER MAPPING FOR public SERVER test0 OPTIONS (user 'postgres');
CREATE USER MAPPING FOR public SERVER test1 OPTIONS (user 'postgres');
CREATE FOREIGN TABLE t0 (id integer not null, constraint id_check check
(id<0) ) SERVER test0 OPTIONS (table_name 't');
CREATE FOREIGN TABLE t1 (id integer not null, constraint id_check check
(id>=0)) SERVER test1 OPTIONS (table_name 't');
create table t (id integer not null) partition by range (id);
alter table t ATTACH PARTITION t0 for values from (MINVALUE) to (0);
alter table t ATTACH PARTITION t1 for values from (0) to (MAXVALUE);
insert into t (id) values (-1);
update t set id=2 where id=-1;

Expected: row in t1 partition.
Reality:
test=# update t set id=2 where id=-1;
ERROR: new row for relation "t" violates check constraint "id_check"
DETAIL: Failing row contains (2).
CONTEXT: remote SQL command: UPDATE public.t SET id = 2 WHERE ((id =
(-1)))

I don't know is this case supposed to work or not, and I can't find any
related notes in documentation.

Unfortunately, this is not supported as documented in the notes section
of the UPDATE reference page [1]https://www.postgresql.org/docs/11/sql-update.html:

"Currently, rows cannot be moved from a partition that is a foreign
table to some other partition, but they can be moved into a foreign
table if the foreign data wrapper supports it."

Best regards,
Etsuro Fujita

[1]: https://www.postgresql.org/docs/11/sql-update.html