Subquery Factoring

When I wrote a note last week about the fixes to the subquery factoringoptimizer code in 11.2.0.3, I finished with a comment about having more to say on the test case if I materialized the subquery. Today’s the day to talk about it. As a reminder, here’s the query, but with the /*+ materialize */ hint in place:

with subq as (
	select
	/*+ materialize */
		outer.*
	from
		emp outer
	where
		sal > 1000000
	and	outer.sal > (
			select
				avg(inner.sal)
 			from	emp inner
			where	inner.dept_no = outer.dept_no
		)
	)
select	*
from	subq
;

Here are the three plans – from 10.2.0.5, 11.1.0.7, and 11.2.0.3 respectively:

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