anchor.diff:  // https://msdn.microsoft.com/en-us/library/ms190273.aspx
   alter_table
       : ALTER TABLE table_name (SET '(' LOCK_ESCALATION '=' (AUTO | TABLE | DISABLE) ')'
  -                             | ADD column_def_table_constraint) ';'?
  +                             | ADD column_def_table_constraint
  +                             | DROP CONSTRAINT constraint=id
  +							 | WITH CHECK ADD CONSTRAINT constraint=id FOREIGN KEY '(' fk = column_name_list ')' REFERENCES table_name '(' pk = column_name_list')'
  +							 | CHECK CONSTRAINT constraint=id
  +							 ) 
  +							 ';'?
       ;
   
   // https://msdn.microsoft.com/en-us/library/ms174269.aspx
  
positive.code: 
  // https://msdn.microsoft.com/en-us/library/ms188783.aspx
  create_index
      : CREATE UNIQUE? clustered? INDEX id ON table_name_with_hint '(' column_name_list ')' ';'?
      ;
  
  // https://msdn.microsoft.com/en-us/library/ms187926(v=sql.120).aspx
  
negative.code: 
  // https://msdn.microsoft.com/en-us/library/ms176118.aspx
  drop_index
      : DROP INDEX (IF EXISTS)? name=id (ON table_name)? ';'?
      ;
  
  // https://msdn.microsoft.com/en-us/library/ms174969.aspx
  