anchor.diff:      : PERIOD FOR SYSTEM_TIME LP_ columnName COMMA_ columnName RP_
       ;
   
  -alterTableOp
  -    : ALTER TABLE tableName
  -    ;
  -
   alterColumn
       : modifyColumnSpecification
       ;
   
   modifyColumnSpecification
  -    : alterColumnOp dataType (COLLATE collationName)? (NULL | NOT NULL)? SPARSE?
  -    ;
  -
  -alterColumnOp
  +    : alterColumnOperation dataType (COLLATE collationName)? (NULL | NOT NULL)? SPARSE?
  +    ;
  +
  +alterColumnOperation
       : ALTER COLUMN columnName
       ;
   
  
positive.code:     ;
  
  alterTable
      : alterTableOp
      (
          alterColumn
          | addColumnSpecification
          | alterDrop
          | alterCheckConstraint
          | alterTrigger
          | alterSwitch
          | alterSet
          | alterTableTableOption
          | REBUILD
      )
      ;
  
  alterIndex
  
negative.code:     (FILESTREAM_ON (ignoredIdentifier_ | schemaName | STRING_))?
      ;
  
  createIndexSpecification_
      : UNIQUE? (CLUSTERED | NONCLUSTERED)?
      ;
  
  alterClause_
      : alterColumn | addColumnSpecification | alterDrop | alterCheckConstraint | alterTrigger | alterSwitch | alterSet | alterTableTableOption | REBUILD
      ;
  
  
  
  