Re: Unique constraint and NULL values

Frank Piron wrote:

  > Yes, but it's a matter of convention because "NULL <> NULL" evaluates
> to null and thus is also not true. So two null values should never
> be considered different.
>

>> ++ mcs

Two nulls should never be evaluated ... there is nothing to consider. So considering them the same or different is irrelevant.

CREATE TABLE t (
col1 NUMBER(1),
col2 VARCHAR2(1),
col3 DATE);

INSERT INTO t (col1) VALUES (1);
COMMIT; What sense would it make to compare col2 and col3? Would you consider them the same?

-- 
Daniel A. Morgan
University of Washington
damorgan_at_x.washington.edu
(replace 'x' with 'u' to respond)