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Re: NULL values seem to short-circuit my unique index - Mailing list pgsql-general

From Chris
Subject Re: NULL values seem to short-circuit my unique index
Date
Msg-id 48E044AF.9040104@gmail.com
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In response to NULL values seem to short-circuit my unique index  (Matthew Wilson <matt@tplus1.com>)
Responses Re: NULL values seem to short-circuit my unique index  (Alban Hertroys <dalroi@solfertje.student.utwente.nl>)
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Matthew Wilson wrote:
> I'm trying to comprehend how NULL values interact with unique indexes.
> It seems like I can insert two rows with NULL values in a column with a
> unique constraint just fine.
>
> Is there something special about NULL?  Can anyone post some links to
> explain what is going on?

When you think of null as "unknown", it makes sense.

Does an unknown value equal another unknown value?

http://www.postgresql.org/docs/8.3/interactive/functions-logical.html

http://www.postgresql.org/docs/8.3/interactive/functions-comparison.html

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