From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Postgres-Bugs <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: Failure to coerce unknown type to specific type |
Date: | 2015-05-01 12:42:45 |
Message-ID: | CA+TgmoaUNFTvUnmV3Fj+kK-TyjVN_S0zNSD_hMBYP8kMCo1d3g@mail.gmail.com |
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On Fri, May 1, 2015 at 1:50 AM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
> On Wed, 2015-04-29 at 15:37 -0700, Tom Lane wrote:
>> We should IMO, but there's been push-back about backwards compatibility
>> when this has been proposed in the past. But I'd rather break backwards
>> compatibility to the extent of saying "you can't do that" than to try to
>> make unknown a full-fledged type, which is what this patch wants to do.
>
> My intention was to make can_coerce_type and coerce_type consistent --
> right now, coerce_type can fail after can_coerce_type returns true.
>
> (I also wanted to improve the composability of subqueries, but I got
> enough resistance that I'm setting that argument aside.)
>
> It really has nothing to do with creating real tables with real columns
> of type unknown.
>
> => select u=t from (select 'x' as u, 'y'::text as t) s;
> ERROR: failed to find conversion function from unknown to text
>
> That's an elog (not an ereport, just plain elog) for what is a
> high-level query compilation error of a fairly sane-looking query, which
> seems wrong.
>
> The code comment above the error says that the caller blew it, but as
> far as I can tell there's nothing the caller can do about it. That seems
> wrong, too.
I agree. I'm not sure what the right fix is, but that query should
probably work, and if it must fail, it certainly shouldn't elog().
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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