anchor.diff:      : columnDefinition | virtualColumnDefinition
       ;
   
  +columnProperties
  +    : columnProperty+
  +    ;
  +
  +columnProperty
  +    : objectTypeColProperties
  +    ;
  +
  +objectTypeColProperties
  +    : COLUMN columnName substitutableColumnClause
  +    ;
  +
  +substitutableColumnClause
  +    : ELEMENT? IS OF TYPE? LP_ ONLY? dataTypeName_ RP_ | NOT? SUBSTITUTABLE AT ALL LEVELS
  +    ;
  +
   modifyColumnSpecification
       : MODIFY (LP_? modifyColProperties (COMMA_ modifyColProperties)* RP_? | modifyColSubstitutable)
       ;
  
positive.code:     : tableName alias? (COMMA_ tableName alias?)*
      ;
  
  
  
  
  
  
  
  tableProperties
      : columnProperties? (AS unionSelect)?
      ;
  
  unionSelect
      : matchNone
      ;
  
  alterTableProperties
  
negative.code:     : CHECKPOINT NUMBER_
      ;
  
  renameColumnClause
      : RENAME COLUMN columnName TO columnName
      ;
  
  