anchor.diff:      ;
   
   columnClauses
  -    : opColumnClause+
  -    | renameColumn
  +    : opColumnClause+ | renameColumn
       ;
   
   opColumnClause
  -    : addColumn
  -    | modifyColumn
  -    | dropColumnClause
  +    : addColumn | modifyColumn | dropColumnClause
       ;
   
   addColumn
  
positive.code:     ;
  
  constraintOption
      : constraintWithName
      | constraintPrimaryOrUnique
      ;
  
  constraintPrimaryOrUnique
      : primaryKey
      | UNIQUE columnList
      ;
  
  renameConstraintClause
  
negative.code:     ;
  
  constraintClauses
      : addConstraintClause | modifyConstraintClause | renameConstraintClause | dropConstraintClause+
      ;
  
  addConstraintClause
  