Re: composite Unique constraint and null

  • From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
  • To: jkstill@xxxxxxxxx
  • Date: Tue, 18 Oct 2005 13:52:07 -0600

Interestingly enough, even though one "null" does not equal another "null", i.e. any comparison with NULL is always false, a unique index on (col1, col2) throws a unqiue constraint violation when you insert a second (1,null). It appears that for the index (1,null) IS equal to (1,null) - or does the unique index use reverse logic and checks if (1,null) <> (1,null) and, since this is false, concludes that (1,null) must be equal (1,null) and therefore violate the constraint ;-)

Jared Still wrote:

A unique constraint can be used for this.

Have you tried it?

Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist

-- Regards

Wolfgang Breitling
Centrex Consulting Corporation

Other related posts: