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Re: BUG #2503: Query results differ based on record count of unrelated table.

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Russell Francis <rfrancis(at)ev(dot)net>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #2503: Query results differ based on record count of unrelated table.
Date: 2006-06-29 13:56:16
Message-ID: 20060629135616.GD1388@surnet.cl (view raw or flat)
Thread:
Lists: pgsql-bugs
Russell Francis wrote:

> If a SELECT statement contains a table in it's FROM clause which has 0
> records in it, the query will not return any results.  If a record is added
> to the table even though it shouldn't modify the results of query, the query
> will return the expected result.
> 
> The SQL statements below are a trimmed down test case which duplicates this
> issue.  The identical SELECT statements return different results depending
> on the record count of the unrelated table_b.
> 
> SELECT table_a.* FROM table_a, table_b WHERE table_a.ta_col_a > 0;

table_b is certainly not unrelated, as it appears in the FROM clause.
So the query is correct to not show any result, per definition of
cartesian product.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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