From: Perrin Harkins
Date: February 25 2010 3:19pm
Subject: Re: EXPLAIN says DEPENDENT SUBQUERY despite no free variables
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On Thu, Feb 25, 2010 at 2:48 AM, Dan Nelson <dnelson@stripped> wrote:
> IN is fine ( for example ... WHERE field1 IN (1,2,3,4,5,6) is extremely
> efficient);

Yes, I meant to say IN/NOT IN subqueries, not value lists.

> it's subqueries in general that are killers.

Subqueries in the FROM clause (aka derived tables) work pretty well,
acting as an in-line temp table.  Other subqueries perform poorly, as
you say.

- Perrin