Abstracts queries fail without seeded data in Scores

[obfuscurity]

Because of the way Postgres handles negation with nulls (e.g. NOT IN), it's not possible to run a query like the following without a seeded entry in the Score table.

SELECT abstracts.*, speakers.full_name AS speaker, 
               speakers.email, events.name AS event_name
FROM abstracts, speakers, events, scores
WHERE ((abstracts.speaker_id = speakers.id)
    AND (abstracts.event_id = events.id)
    AND ((scores.abstract_id != abstracts.id)
        OR (scores.judge != 'jdixon')))
ORDER BY abstracts.id

Demonstration showing a successful query when at least one Score exists. Note that it works for all users regardless of whether they have a score recorded or not.

[20] pry(main)> Score.insert(:judge => 'jdixon', :count => 0, :abstract_id => 81)
=> 2
[21] pry(main)> Score.all
=> [#<Score @values={:id=>2, :judge=>"jdixon", :count=>0, :abstract_id=>81}>]
[22] pry(main)> Abstract.fetch_one_random_unscored_by_user('jdixon').id
=> 26
[23] pry(main)> Abstract.fetch_one_random_unscored_by_user('whilp').id
=> 53

Demonstration showing failed queries when no scores exist.

[26] pry(main)> Score.first.destroy
=> #<Score @values={:id=>2, :judge=>"jdixon", :count=>0, :abstract_id=>81}>
[27] pry(main)> Score.all
=> []
[28] pry(main)> Abstract.fetch_one_random_unscored_by_user('jdixon').id
=> nil
[29] pry(main)> Abstract.fetch_one_random_unscored_by_user('whilp').id
=> nil

One last time, proving that the simple existence of a Score is sufficient to workaround this issue.

[30] pry(main)> Score.insert(:judge => 'jdixon', :count => 0, :abstract_id => 81)
=> 3
[31] pry(main)> Score.all
=> [#<Score @values={:id=>3, :judge=>"jdixon", :count=>0, :abstract_id=>81}>]
[32] pry(main)> Abstract.fetch_one_random_unscored_by_user('jdixon').id
=> 4
[33] pry(main)> Abstract.fetch_one_random_unscored_by_user('whilp').id
=> 19

[obfuscurity]

I'd prefer to fix this somehow in the SQL, if possible. The alternative would be to handle the exclusion in application code by pulling Score.all separately and coalescing the results.