From: Perrin Harkins
Date: June 2 2010 5:49pm
Subject: Re: how to avoid sub-query to gain performance
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On Wed, Jun 2, 2010 at 10:28 AM, Lin Chun <franks1984@stripped> wrote:
> *don't know it very clear, but i think is the problem of <derived> seems it
> take full scaning*

Yes, it has no indexes so it isn't good for very large subqueries.
You should create them as temporary tables instead and give them
indexes.

- Perrin