The Oracle WITH clause is one of the most commonly used techniques to simplify the SQL source code and improve performance. In Oracle SQL, the ‘WITH’ clause also known as a Common Table Expression (CTE) is a powerful tool which is also used to enhance the code readability.
WITH is commonly used to define temporary named result sets, also referred to as subqueries or CTEs as defined earlier. These temporary named sets can be referenced multiple times within the main SELECT SQL query. The CTEs are like virtual tables and are very helpful in organizing and modularizing the SQL code.