Written by David Ducos for Percona. We usually try to avoid subselects because sometimes they force the use of a temporary table and limits the use of indexes. But, when is good to use a subselect?
from My Pocket http://feeds.dzone.com/~r/dzone/frontpage/~3/KiiGMR1DpNU/speed_up_group_by_queries_with_subselects_in_mysql.html datadb, php
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