Subqueries using SQL derived tables

A SQL derived table can be used in a subquery from clause. For example, this query finds the names of the publishers who have published business books:

select pub_name from publishers
   where "business" in
      (select type from
         (select type from titles, publishers
             where titles.pub_id = publishers.pub_id)
       dt_titles)

Here, dt_titles is the SQL derived table defined by the innermost select statement.