請問PHP問題！

Strictly speaking this is not a PHP question.

Your code cannot have access to Yahoo database unless Yahoo opens a port and give you the credentials to access its server, which is quite unlikely.

Requesting information from another vendor is achieved by making remote procedure calls to the vendor. This is like calling a function but only in this case the function is on the vendor's remote server. The remote function returns the required information, usually in XML format. These days these remote procedure calls are called web services, which allow one server to call upon the services of another server.

Visit this Yahoo site to see what Yahoo API's are available for developers.
http://developer.yahoo.com/