Re: BUG #6626: union all with values of type "unknown"

2012/5/22 Robert Haas <robertmhaas(at)gmail(dot)com>:
> On Tue, May 22, 2012 at 3:55 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>>> deik3qfhu265n6=> with hello as (select 'hello' as name)
>>>> deik3qfhu265n6-> , bye as (select 'bye' as name)
>>>> deik3qfhu265n6-> select * from hello UNION ALL select * from bye;
>>>> ERROR:  failed to find conversion function from unknown to text
>>
>>> I think it should return a column of type text, just as if you'd done this:
>>> select v from (select 'hello' union all select 'bye') x(v);
>>
>> I don't think it's a great idea to make CTEs handle this differently
>> from other places where the same issue arises (from memory, views and
>> INSERT/SELECT have problems with unknown literals, and there are
>> probably other places I'm forgetting).
>>
>> Should we institute a uniform policy of forcing unknown sub-select
>> outputs to text type?  This would almost certainly break a few peoples'
>> queries, but the reduction of surprise might be worth it for most.
>
> I think if we can't do real type inference, forcing unknown to text is
> probably the least of evils.

can we implement late cast? Cast unknown to text only when exception
is raised, resp. before? This issue is relative unfriendly for
beginners

Regards

Pavel
>
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> Robert Haas
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