For some flattened subqueries, certain join orders are possible only if a sort is later used to remove duplicate results. When one of these join orders is considered, the following message is printed right after the join permutation order is printed:
2 - 0 - 1 - This join order created while converting an exists join to a regular join, which can happen for subqueries, referential integrity, and select distinct.
For more information on subqueries and join orders, see “Flattened subqueries using duplicate elimination” on page 134 in Performance and Tuning: Optimizer.
