The following bug has been logged on the website:
Bug reference: 7501
Logged by: Matt Kusnierz
Email address: matthew.p.kusnierz@jpmorgan.com
PostgreSQL version: 9.0.4
Operating system: Windows XP
Description: =
Multi-column unique indexes allow duplicate rows to be inserted if any of
the indexed columns are inserted with a null.
For example:
create table foo (a varchar(10) null, b varchar(10) null);
create unique index uix on foo (a, b);
insert into foo (a, b) values ('abc', null);
insert into foo (a, b) values ('abc', null);
Clearly the second insert should fail with an ERROR: duplicate key value
violates unique constraint "uix"
But this does not occur!