What is the difference between IN and EXISTS?

IN: evaluates all values in the subquery result set, then checks membership. If subquery returns NULLs: NOT IN returns empty result. Performance depends on list size. EXISTS: evaluates the subquery and returns TRUE on FIRST match (short-circuit). Always safe with NULLs. Generally preferred for large sets or when membership (not the values) is what matters. Use IN when the subquery returns a small,