Many developers think that correlated subquires are not efficient.

The correct answer starts with "It depends on...".
Sometimes we can achieve the same efficient perfomance
what we can do with inline views.
Let's see the following example:
(Who earns more then his/her departments's average salary?)

SELECT  e.last_name, e.department_id, e.salary  FROM employees e
WHERE e.salary> (SELECT AVG(salary) FROM employees where
department_id=e.department_id );

SQL_ID  3jr7194pfhh3s, child [...]