Examine this statement and its corresponding execution plan:Which phase introduces the CONCATENATION step?

The CONCATENATION step in an execution plan is introduced during the SQL Transformation phase. This phase is part of the optimizer's query transformations which can include various techniques to rewrite the query for more efficient execution. The CONCATENATION operation is used to combine the results of two separate SQL operations, typically when there is an OR condition in the WHERE clause, as seen in the provided query.

References:

Oracle Database SQL Tuning Guide, 19c

Oracle Database Concepts, 19c