Re: Check constraints on non-immutable keys

On Wed, Jun 30, 2010 at 6:57 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Peter Eisentraut <peter_e@gmx.net> writes:
>> <kibo>
>> "The <search condition> shall simply contain a <boolean value
>> expression> that is retrospectively deterministic."
>
>> This is then defined in a rather complex manner that ends up disallowing
>> col > now() but allowing col < now().
>> </kibo>
>
> Oh, cute.  Seems to have been added in SQL:2003.  I guess somebody
> nagged them about wanting to be able to write CHECK(col <= now()).
> The detailed definition is amazingly laborious and yet limited, though,
> as it basically doesn't address the problem except for that specific
> case and close relatives.

Well, solving the problem in general is equivalent to the halting problem, so...

--
Robert Haas
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