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BUG #3308: Nested outer join gives wrong results

From: "George Sakkis" <george(dot)sakkis(at)gmail(dot)com>
To: pgsql-bugs(at)postgresql(dot)org
Subject: BUG #3308: Nested outer join gives wrong results
Date: 2007-05-25 20:24:40
Message-ID: 200705252024.l4PKOern055836@wwwmaster.postgresql.org (view raw or flat)
Thread:
Lists: pgsql-bugs
The following bug has been logged online:

Bug reference:      3308
Logged by:          George Sakkis
Email address:      george(dot)sakkis(at)gmail(dot)com
PostgreSQL version: 8.2.3
Operating system:   Linux
Description:        Nested outer join gives wrong results
Details: 

I have the following two subqueries, both returning a single column q_id;
also the result set of A is a strict superset of B:

Query A
-------
SELECT query.id as q_id
FROM ranker, run, query
WHERE ranker.id = 72 AND 
      run.id = ranker.run_id AND 
      query.set_id = run.set_id

(966 rows)

Query B
-------
SELECT serp_result.q_id
FROM serp_result LEFT OUTER JOIN editor_rating using (q_id,norm_url)
WHERE serp_result.ranker_id = 72 AND 
      serp_result.rank <= 1 
      AND editor_rating.grade is null

(251 rows)


Now, the left outer join of A and B should be equal to A in this case since
A is a superset of B. If I save A in a temp table and use this for the join,
that's indeed the result:

SELECT query.id as q_id INTO TEMP t1
FROM ranker, run, query
WHERE ranker.id = 72 AND 
      run.id = ranker.run_id AND 
      query.set_id = run.set_id

SELECT *
FROM t1
LEFT JOIN (
  SELECT serp_result.q_id
  FROM serp_result LEFT OUTER JOIN editor_rating using (q_id,norm_url)
  WHERE serp_result.ranker_id = 72 AND serp_result.rank <= 1 AND
editor_rating.grade is null
) AS t2 USING (q_id)
;

(966 rows)

Likewise if I save B into a temp table and join with A:

SELECT serp_result.q_id into TEMP t2
FROM serp_result LEFT OUTER JOIN editor_rating using (q_id,norm_url)
WHERE serp_result.ranker_id = 72 AND serp_result.rank <= 1 AND
editor_rating.grade is null

SELECT *
FROM (
  SELECT query.id as q_id
  FROM ranker, run, query
  WHERE ranker.id = 72 AND 
        run.id = ranker.run_id AND 
        query.set_id = run.set_id
) AS t1
LEFT JOIN t2 USING (q_id)

(966 rows)

If I don't use temp tables though, the result is equal to B instead:

SELECT *
FROM (
  SELECT query.id as q_id
  FROM ranker, run, query
  WHERE ranker.id = 72 AND 
        run.id = ranker.run_id AND 
        query.set_id = run.set_id
) AS t1
LEFT JOIN (
  SELECT serp_result.q_id
  FROM serp_result LEFT OUTER JOIN editor_rating using (q_id,norm_url)
  WHERE serp_result.ranker_id = 72 AND 
        serp_result.rank <= 1 
        AND editor_rating.grade is null
) AS t2 USING (q_id)
;

(251 rows)

What gives ?

Responses

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Next:From: Tom LaneDate: 2007-05-25 21:21:52
Subject: Re: BUG #3308: Nested outer join gives wrong results
Previous:From: Tom LaneDate: 2007-05-25 14:38:51
Subject: Re: BUG #3307: Software error when accessed

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