A derived table puts a step in the middle of the query. WITH puts it at the top, with a name:

WITH max_budget AS (
  SELECT MAX(budget) AS value
  FROM department
)
SELECT d.dept_name, d.budget
FROM department d, max_budget m
WHERE d.budget = m.value;

• The named query is a common table expression (CTE).
• The statement below WITH uses the name like a table: in FROM, in a join, in a subquery.
• The CTE exists only for this one statement.

Several steps

Separate CTEs with commas. A later CTE can use an earlier one, and the final query can use each of them more than once:

WITH step_one AS (…),
     step_two AS (SELECT … FROM step_one …)
SELECT … FROM step_two …;

The query reads from top to bottom, one step at a time. Use WITH when a query has more than one level.