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  1. Fix attribute mapping for COPY TO on partitioned tables.

  1. Fix bug of COPY TO support partition table

    Chao Li <li.evan.chao@gmail.com> — 2026-05-14T09:59:46Z

    Hi,

I just tested the "Support COPY TO for partitioned tables" patch. While tracing a normal case, I noticed this suspicious code:
```
	/*
	 * If we are exporting partition data here, we check if converting tuples
	 * to the root table's rowtype, because a partition might have column
	 * order different than its root table.
	 */
	if (root_rel != NULL)
	{
		root_slot = table_slot_create(root_rel, NULL);
		map = build_attrmap_by_name_if_req(RelationGetDescr(root_rel),   <<== input is root table
										   RelationGetDescr(rel), <== output is partition
										   false);
	}

	while (table_scan_getnextslot(scandesc, ForwardScanDirection, slot))
	{
		TupleTableSlot *copyslot;

		CHECK_FOR_INTERRUPTS();

		if (map != NULL)
			copyslot = execute_attr_map_slot(map, slot, root_slot); <== input is partition, output is root table
		else
		{
			/* Deconstruct the tuple */
			slot_getallattrs(slot);
			copyslot = slot;
		}
```

The code comment says that partition tuples should be converted to the root table's rowtype before output. Also, `execute_attr_map_slot()` takes the partition slot as input and the root slot as output. However, the attribute map is built in the opposite direction, with the root relation as input and the partition relation as output.

In normal cases, partitions have the same attribute list as the root table, so this bug is not triggered. I built the following repro by dropping a column from the partition, which makes the partition’s physical tuple descriptor different from the root table's descriptor:
```
evantest=# create table p (a int, b int) partition by range (a);
CREATE TABLE
evantest=# create table c (x int, a int, b int);
CREATE TABLE
evantest=# alter table c drop column x;
ALTER TABLE
evantest=# alter table p attach partition c for values from (1) to (10);
ALTER TABLE
evantest=# insert into p values (1, 11), (2, 22);
INSERT 0 2
evantest=# copy p to stdout;
\N	\N
\N	\N
```

As shown above, COPY incorrectly outputs all NULLs.

The fix is straightforward, just reverse the order of `rel` and `root_rel` when calling `build_attrmap_by_name_if_req()`. After the fix, COPY works correctly:
```
evantest=# copy p to stdout;
1	11
2	22
```

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

  2. Re: Fix bug of COPY TO support partition table

    Fujii Masao <masao.fujii@gmail.com> — 2026-05-14T16:25:11Z

    On Thu, May 14, 2026 at 7:00 PM Chao Li <li.evan.chao@gmail.com> wrote:
> As shown above, COPY incorrectly outputs all NULLs.

Good catch!

> The fix is straightforward, just reverse the order of `rel` and `root_rel` when calling `build_attrmap_by_name_if_req()`. After the fix, COPY works correctly:

Thanks for the patch! It looks good to me.

Regards,

-- 
Fujii Masao

  3. Re: Fix bug of COPY TO support partition table

    Masahiko Sawada <sawada.mshk@gmail.com> — 2026-05-14T16:36:21Z

    On Thu, May 14, 2026 at 9:25 AM Fujii Masao <masao.fujii@gmail.com> wrote:
>
> On Thu, May 14, 2026 at 7:00 PM Chao Li <li.evan.chao@gmail.com> wrote:
> > As shown above, COPY incorrectly outputs all NULLs.
>
> Good catch!

Yeah, it should be fixed. Thank you for the report!

>
> > The fix is straightforward, just reverse the order of `rel` and `root_rel` when calling `build_attrmap_by_name_if_req()`. After the fix, COPY works correctly:
>
> Thanks for the patch! It looks good to me.
>

LGTM too. I'll take care of it as this is my commit, if you're okay
with it, Fujii-san.

Regards,


--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com

  4. Re: Fix bug of COPY TO support partition table

    Fujii Masao <masao.fujii@gmail.com> — 2026-05-14T16:56:52Z

    On Fri, May 15, 2026 at 1:37 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> LGTM too. I'll take care of it as this is my commit, if you're okay
> with it, Fujii-san.

Yes, please go ahead!

Regards,

-- 
Fujii Masao

  5. Re: Fix bug of COPY TO support partition table

    Masahiko Sawada <sawada.mshk@gmail.com> — 2026-05-14T18:03:36Z

    On Thu, May 14, 2026 at 9:57 AM Fujii Masao <masao.fujii@gmail.com> wrote:
>
> On Fri, May 15, 2026 at 1:37 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > LGTM too. I'll take care of it as this is my commit, if you're okay
> > with it, Fujii-san.
>
> Yes, please go ahead!

Pushed.

Regards,

-- 
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com