A derived table is a result of access to a stored table during query execution. It can be:
The result set generated by the query
An intermediate result during query execution; that is, the result of the join of the first two tables in the join order, which is then joined with a third table
Derived tables result from one of the scan operators that specify the access method: scan, i_scan, or t_scan, for example, (i_scan title_id_ix titles).
