anchor.diff:      ;
   
   group_by_clause
  -    : GROUP BY (','? group_by_elements)+ having_clause?
  -    | having_clause (GROUP BY (','? group_by_elements)+)?
  +    : GROUP BY group_by_elements (',' group_by_elements)* having_clause?
  +    | having_clause (GROUP BY group_by_elements (',' group_by_elements)*)?
       ;
   
   group_by_elements
  
positive.code:     ;
  
  using_clause
      : USING (ASTERISK | (','? using_element)+)
      ;
  
  using_element
  
negative.code:     ;
  
  table_ref_list
      : table_ref (',' table_ref)*
      ;
  
  // NOTE to PIVOT clause
  