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Re: many Union all vs. inserting results to temp table

From: Joel Garry <joel-garry_at_home.com>
Date: 23 Mar 2006 14:52:25 -0800
Message-ID: <1143154345.388515.71050@z34g2000cwc.googlegroups.com>


Oh yeah, I forgot the part about unions doing sort and distincts. Quoting asktom:

"A union B union C

is really

distinct( sort( a + b + c ) )"

So at some point you would expect to see severe performance degradation as the sort segments get written to disk.

jg

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Received on Thu Mar 23 2006 - 16:52:25 CST

Original text of this message

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