anchor.diff:      | SYSTEM_VERSIONING EQ_ ON (LP_ HISTORY_TABLE EQ_ tableName (COMMA_ DATA_CONSISTENCY_CHECK EQ_ (ON | OFF))? RP_)?
       ;
   
  +tableExistClause_
  +    : (IF EXISTS)?
  +    ;
  +
  +indexExistClause_
  +    : (IF EXISTS)?
  +    ;
   
   
   
  
positive.code:     : UNIQUE? (CLUSTERED | NONCLUSTERED)?
      ;
  
  alterClause_
      : modifyColumnSpecification | addColumnSpecification | alterDrop | alterCheckConstraint | alterTrigger | alterSwitch | alterSet | alterTableOption | REBUILD
      ;
  
  
negative.code:     ;
  
  alterTable
      : ALTER TABLE tableName alterDefinitionClause_
      ;
  
  alterIndex
  