Difference between EXISTS and IN in SQL?

Question

What is the difference between the EXISTS and IN clause in SQL?

When should we use EXISTS, and when should we use IN

Answer 1

My understand is both should be the same as long as we are not dealing with NULL values.

The same reason why the query does not return the value for = NULL vs is NULL. http://sqlinthewild.co.za/index.php/2010/02/18/not-exists-vs-not-in/

As for as boolean vs comparator argument goes, to generate a boolean both values needs to be compared and that is how any if condition works.So i fail to understand how IN and EXISTS behave differently .