Here are the sample tables for my question.

CREATE TABLE bar (
    id        int2 PRIMARY KEY UNIQUE DEFAULT nextval('bar_id_seq'),
    ...
);

CREATE TABLE foo (
    id        int2 PRIMARY KEY UNIQUE DEFAULT nextval('foo_id_seq'),
    number    int2 NOT NULL,
    bar_id    int2 REFERENCES bar ON UPDATE CASCADE ON DELETE CASCADE,
    ...
);
CREATE UNIQUE INDEX foo_number_id_index ON foo(number, bar_id);

I am a novice for sure. I am trying to prevent multiple combinations
of the number and bar_id fields. However, since the bar_id can be NULL
I am actually getting multiple combinations with NULL. 

For example, 
foo:
id     number    bar_id .....
-------------------------------
1    |    1    | 
2    |    2    |   3
3    |    1    |   
....

Row 1 and 3 are duplicates that I wish to disallow. I am however seeing
just this behavior with 7.3.2. I am seeing the duplicates. I am not able
to add another row with number = 2 and bar_id = 3. 

What am I doing wrong? What sort of NULLism is biting me?

I have searched around the lists and the documentation, I am sure it is
explained but I am not able to see the solution. I link that helps out
would be appreciated.

Thanks for your help.

Matthew

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