Re: Postgres 11: Table Partitioning and Primary Keys

On Mon, Jul 08, 2019 at 10:37:37PM -0400, Bruce Momjian wrote:
> On Fri, Jul 5, 2019 at 09:20:07PM +0000, PG Doc comments form wrote:
>> In the documentation for Postgres 11 table partitioning, there is no mention
>> of the requirement that the Primary Key of a partitioned table must contain
>> the partition key.
>> In fact the documentation on primary keys is so light that I am not even
>> 100% sure the above is correct. If the following table is not possible in
>> Postgres 11, the documentation should find some way to make that clear.
>>
>> I believe this should be documented in section "5.10.2.3. Limitations"
>
> Can someone comment on this? CC to hackers.

Yep, that's the case:
=# CREATE TABLE parent_tab (id int, id2 int primary key)
PARTITION BY RANGE (id);
ERROR: 0A000: insufficient columns in PRIMARY KEY constraint
definition
DETAIL: PRIMARY KEY constraint on table "parent_tab" lacks column
"id" which is part of the partition key.
LOCATION: DefineIndex, indexcmds.c:894

I agree with the report here that adding one sentence to 5.10.2.3
which is for the limitations of declarative partitioning would be a
good idea. We don't mention the limitation in CREATE TABLE either
(which would be rather incorrect IMO).

Attached is an idea of patch for the documentation, using this
wording:
+ <listitem>
+ <para>
+ When defining a primary key on a partitioned table, the primary
+ key column must be included in the partition key.
+ </para>
+ </listitem>
If somebody has any better idea for that paragraph, please feel free.
--
Michael