mysql diff and add diff records into new database
mysqldump --insert-ignore --extended-insert=FALSE  --complete-insert 
  --skip-disable-keys --no-create-info -h A --port=3306 -u A 
  --password=A database_A table_A | mysql -h B -u B --password=B database_B

--insert-ignore eventually worked as diff and made the rows unique while dumping data across database.