Joe Celko's SQL for Smarties, 3rd Edition

15.2. EXISTS and INNER JOINs

The [NOT] EXISTS predicate is almost always used with a correlated subquery. Very often the subquery can be “flattened” into a JOIN, which will frequently run faster than the original query. Our sample query can be converted into:

SELECT P1.emp_name, ' has the same birthday as a famous person!'
  FROM Personnel AS P1, Celebrities AS C1
 WHERE P1.birthday = C1.birthday;

The advantage of the JOIN version is that it allows us to show columns from both tables. We should make the query more informative by rewriting it:

SELECT P1.emp_name, ' has the same birthday as ', C1.emp_name
  FROM Personnel AS P1, Celebrities AS C1
 WHERE P1.birthday = C1.birthday;

This new query could be written with an EXISTS() predicate, but that is ...