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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Etsuro Fujita <etsuro.fujita@gmail.com>
cc: Ibrar Ahmed <ibrar.ahmad@gmail.com>,
        PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
        Neil Chen <carpenter.nail.cz@gmail.com>
Subject: Re: BUG #16583: merge join on tables with different DB collation
 behind postgres_fdw fails
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Comments: In-reply-to Etsuro Fujita <etsuro.fujita@gmail.com>
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Etsuro Fujita <etsuro.fujita@gmail.com> writes:
> On Sat, Sep 25, 2021 at 4:11 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Longer-term, it seems like we really have to be able to represent
>> the notion of a remote column that has an "unknown" collation (that
>> is, one that doesn't match any local collation, or at least is not
>> known to do so).

> +1

> In addition, a) we should detect whether local “default” matches
> remote “default”,

If we had a way to do that, most of the problem here wouldn't exist.
I don't believe we can do it reliably.  (Maybe we could put it on
the user to tell us, say via a foreign-server property?)

			regards, tom lane