Correlated Nested Query (SQL)

A correlated nested query is where the condition in the WHERE clause of a nested query references an attribute of a relation declared in the outer query. The result of a correlated nested query is different for each tuple of the relation in the outer query.

SELECT E.name
FROM   EMPLOYEE AS E
WHERE  E.ssn IN (
	SELECT essn
	FROM   DEPENDENT
	WHERE  essn=E.ssn
	  AND  E.name=dependent_name
)

Although these can still be re-written as a single block query with a simple Join Condition (SQL).