Based on logic in the code, the example query isn't flattenable. . .
That's because whoever wrote the code made it handle only the
simplest case. I doubt it would be hard to make it flatten many other
types of table subqueries.
My general philosophy toward query performance issues is that I
prefer massaging the query into a standard form and letting the
optimizer handle it to putting in special-case logic for certain
types of queries. The optimizer can do things the rest of query
processing would have a difficult time with. For example, if an inner
join in a subquery is flattened into the outer query, the optimizer
is free to put the tables from the subquery anywhere in the join
order, even if it means interspersing the subquery's tables with the
outer query's tables.
- Jeff Lichtman
[EMAIL PROTECTED]
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