On 17 April 2011 00:40, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Thom Brown <thom@linux.com> writes:
>> On 16 April 2011 23:23, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> Does anyone think it's not a bug that ALTER TABLE lets this through?
>>> If so, what do you think the querying semantics ought to be?
>
>> An argument to not treat it as a bug might be to suggest that the
>> child table's column could inherit the parent table's column collation
>> when the query targets the parent, but revert to its own otherwise.
>
> That seems to me to be about on par with arguing that inheritance
> shouldn't demand column type matching, but should coerce child columns
> on-the-fly to their parent's type. Even if you don't think that's
> horrid from a theoretical standpoint, there's a good practical reason
> not to allow it: if it acts that way, then indexes on the child column
> will silently not be usable for many kinds of query against the parent.
> People will be tearing their hair out looking for the cause of their
> performance problems ... and, no doubt, filing bugs against the planner
> ... when throwing an error would have helped them catch the mismatch.
>
> I think there needs to be a pretty darn compelling use-case for such
> mismatches before we should allow them. And I don't see one.
Conceded.
--
Thom Brown
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