Re: Unique Constraint with Multiple NULLS

"David Portas" <REMOVE_BEFORE_REPLYING_dportas_at_acm.org> wrote in message <news:G_2dncia7cWZCGmiRVn-uw_at_giganews.com>...

> > What is the SQL-92 standard for allowing multiple NULL values within a
> > unique constraint?

> A UNIQUE constraint treats NULLs in the same column as equal to each other.
> In other words UNIQUE(colX) will not be satisfied if colX contains more than
> one NULL value. This is consistent with the behaviour of other grouping
> operations like GROUP BY and DISTINCT.

However, this is also *in*consistent with the = and <> comparison operators within JOIN, WHERE, HAVING, etc. NULL as a concept is horribly broken and ruins the relational model as defined by Codd.

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