When you use a column alias in the WHERE clause to refer to a calculated value, you must use the keyword CALCULATED along with the alias.
You must also use the keyword CALCULATED when you use a column alias in a HAVING clause.

PROC SQL calculates summary functions and outputs results in different ways depending on a combination of factors. Four key factors are (2-26)

• whether the summary function specifies one or multiple columns as arguments
  
  
• whether the query contains a GROUP BY clause
  
  
• if the summary function is specified in a SELECT clause, whether there are additional columns listed that are outside of a summary function
  
  
• whether the WHERE clause, if there is one, contains only columns that are specified in the SELECT clause.