Multi level Nested Query

• Select name from emp X
  where sal >
  (Select sal from Emp
  where Emp.no =
  (Select manager from Emp
  where Emp.no = x.manager ));

• Evaluate from bottom up:
• for each top level val
• for each into level val
• eval nested query.
• In above example 3 is eval only once per top level value.