anchor.diff:      ;
   
   table_ref_list
  -    : table_ref (',' table_ref)*
  +    : (','? table_ref)+
       ;
   
   // NOTE to PIVOT clause
  
positive.code:     ;
  
  rollup_cube_clause
      : (ROLLUP | CUBE) '(' grouping_sets_elements (',' grouping_sets_elements)* ')'
      ;
  
  grouping_sets_clause
      : GROUPING SETS '(' grouping_sets_elements (',' grouping_sets_elements)* ')'
      ;
  
  grouping_sets_elements
  
negative.code: 
  unpivot_clause
      : UNPIVOT ((INCLUDE | EXCLUDE) NULLS)?
      '(' (column_name | paren_column_list) pivot_for_clause unpivot_in_clause ')'
      ;
  
  unpivot_in_clause
      : IN '(' (','? unpivot_in_elements)+ ')'
      ;
  
  unpivot_in_elements
      : (column_name | paren_column_list)
        (AS (constant | '(' (','? constant)+ ')'))?
      ;
  
  hierarchical_query_clause
  