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From: pinker <pinker@onet.eu>
To: pgsql-performance@postgresql.org
Subject: Re: UNION and bad performance
Date: Sun, 8 Jun 2014 06:58:55 -0700 (PDT)
Message-ID: <1402235935505-5806445.post@n5.nabble.com> (raw)
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>> rhaas=# explain select a from generate_series(1,100) a union select a
>> from generate_series(1,100) a;
>>                                      QUERY PLAN
>> --------------------------------------------------------------------------------------
>> HashAggregate  (cost=45.00..65.00 rows=2000 width=4)
>>   ->  Append  (cost=0.00..40.00 rows=2000 width=4)


Why in this case the estimated number of rows is 2000? Is it standard
planner behavior?





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