Date: Mon, 8 Jul 2019 10:31:53 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org,
	Manuel Rigger <rigger.manuel@gmail.com>
Subject: Re: Broken defenses against dropping a partitioning column
Message-ID: <20190708143153.GA5929@alvherre.pgsql>
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On 2019-Jul-07, Tom Lane wrote:

> Ideally, perhaps, a DROP CASCADE like this would not cascade to
> the whole table but only to the table's partitioned-ness property,
> leaving you with a non-partitioned table with most of its data
> intact.  It would take a lot of work to make that happen though,
> and it certainly wouldn't be back-patchable, and I'm not really
> sure it's worth it.

Maybe we can add dependencies to rows of the pg_partitioned_table
relation, with the semantics of "depends on the partitioned-ness of the
table"?

That said, I'm not sure I see the use case for an ALTER TABLE .. DROP
COLUMN command that turns a partitioned table (with existing partitions
containing data) into one non-partitioned table with all data minus the
partitioning column(s).

This seems vaguely related to the issue of dropping foreign keys; see
https://postgr.es/m/20190329152239.GA29258@alvherre.pgsql wherein I
settled with a non-ideal solution to the problem of being unable to
depend on something that did not cause the entire table to be dropped
in certain cases.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services