Re: BUG #17720: pg_dump creates a dump with primary key that cannot be restored, when specifying 'using index ...'

Daniel Gustafsson <daniel(at)yesql(dot)se> writes:
> On 14 Dec 2022, at 13:54, David G. Johnston <david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>> There is a decent chance that the fix here is to prohibit doing what you did here - a PK cannot contain nulls in any of its columns so indeed choosing an index that specifies how nulls behave is non-sensical. That said, it also doesn’t hurt so long as the column itself is indeed not null. But extending the syntax doesn’t seem that appealing.

> Even if we prohibit this, there is still the case of all existing systems which
> can't be dumped. I wonder if the solution is to teach pg_dump to not create
> NULLS NOT DISTINCT primary key constraints? The simple attached fix creates a
> valid PK constraint on the above schema.

It doesn't make sense for pg_dump to editorialize on a schema that
we otherwise consider valid; people would rightfully complain that
dump/restore changed things. So we need to do both things: prohibit
adopting such an index as a PK constraint (but I guess it's okay
for plain unique constraints?), and adjust pg_dump to compensate
for the legacy case where it was already done.

regards, tom lane