Описание тега subquery-factoring
Use this tag for questions related to the subquery factoring, i.e. the WITH clause, a part of the SQL-99 standard.
Most of the tagged questions are related to SQL-like topics and of course, Oracle.
The WITH clause, or subquery factoring clause, is part of the SQL-99 standard and was added into the Oracle SQL syntax in Oracle 9.2. The WITH clause may be processed as an inline view or resolved as a temporary table. The advantage of the latter is that repeated references to the subquery may be more efficient as the data is easily retrieved from the temporary table, rather than being requeried by each reference. You should assess the performance implications of the WITH clause on a case-by-case basis.
Source: WITH Clause: Subquery Factoring