如何使用另一个数据库的转储更新一个数据库 - MySQL

I had made two database with exactly same tables and columns say A and B in mysql. I created dump of database A and then try to update contents of DataBase B using dump of DataBase A. I was using command -->source [path]; ./ What it did that dump of DataBase A completely removed the contents of DataBase B. I was not able figure out how to update one database using dump of another database. Please help me. I had made two database with exactly same table