From: | "J(dot) Greenlees" <jaqui(at)telus(dot)net> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: Unique Index |
Date: | 2005-01-19 23:02:16 |
Message-ID: | 41EEE6F8.7020800@telus.net |
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Thread: | |
Lists: | pgsql-general |
Roman Neuhauser wrote:
> # alex(at)meerkatsoft(dot)com / 2005-01-20 01:35:32 +1100:
>
>>i have a unique index on a table over multiple columns. If now one of
>>the records has a null value in one of the indexed columns i can insert
>>the same record multiple times.
>>
>>Is this a problem within postgres or expected?
>
>
> In SQL, NULL means "unknown value". How could you assert that two
> NULLs are equal?
>
which doesn't make mathematical sense.
mathwise null is an empty result.
so setting the logic up using the math logic, null values are always equal.
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