On 10/01/2018 11:58 AM, Tom Lane wrote:
> Mark Wong <mark@2ndQuadrant.com> writes:
>> a | a | uuid_cmp
>> --------------------------------------+--------------------------------------+-------------
>> 11111111-1111-1111-1111-111111111111 | 11111111-1111-1111-1111-111111111111 | 0
>> 11111111-1111-1111-1111-111111111111 | 22222222-2222-2222-2222-222222222222 | -2147483648
>> 11111111-1111-1111-1111-111111111111 | 3f3e3c3b-3a30-3938-3736-353433a2313e | -2147483648
>> 22222222-2222-2222-2222-222222222222 | 11111111-1111-1111-1111-111111111111 | 1
>> 22222222-2222-2222-2222-222222222222 | 22222222-2222-2222-2222-222222222222 | 0
>> 22222222-2222-2222-2222-222222222222 | 3f3e3c3b-3a30-3938-3736-353433a2313e | -2147483648
>> 3f3e3c3b-3a30-3938-3736-353433a2313e | 11111111-1111-1111-1111-111111111111 | 1
>> 3f3e3c3b-3a30-3938-3736-353433a2313e | 22222222-2222-2222-2222-222222222222 | 1
>> 3f3e3c3b-3a30-3938-3736-353433a2313e | 3f3e3c3b-3a30-3938-3736-353433a2313e | 0
>> (9 rows)
>
> Oooh ... apparently, on that platform, memcmp() is willing to produce
> INT_MIN in some cases. That's not a safe value for a sort comparator
> to produce --- we explicitly say that somewhere, IIRC. I think we
> implement DESC by negating the comparator's result, which explains
> why only the DESC case fails.
>
>
Is there a standard that forbids this, or have we just been lucky up to now?
cheers
andrew
--
Andrew Dunstan https://www.2ndQuadrant.com
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