Rank functions
  
   The functions DENSE_RANK, RANK, and ROW_NUMBER have the following restrictions:
  
  
   • They can only be used in SELECT statements.
  
  
   • They do not support integer indices as ORDER BY clause expressions.
  
  
   • They cannot be used in expressions.
  
  
   • They cannot be used in a Search Condition.
  
  
   • The NTILE rank function is not supported.
  
  
   Note: Set functions in RANK functions are not supported.
  
  Example 
  
   SELECT RANK() OVER (ORDER BY MAX(sal)) FROM emp;
  
  
   See 
DENSE_RANK, 
RANK, and 
ROW_NUMBER for more information.