Hello, I am wondering how do you link multiple My SQL databases together for a website. It is for usernames and passwords so people can register for one thing on the website and be automatically registered for everything else. Thanks, Andrew
I don't think there is a good solution for doing that directly. You can always use triggers to copy the data to other databases and have other triggers for data validation (i.e. consistent passwords). Or you can change the design where there is a user table and everything links off of it.
You can login to multiple databases at one time and http://nz.php.net/manual/en/function.mysql-connect.php shows you how you can have different $link variables to identify each database you have connected to. You'd just need to code the update through each relevant database. The links could even be held in an array so that you could use foreach() to work through each connection without having to be particularly mindful of how many connections there are - which makes it flexible you add/remove sites in the future.
For linking database use key such as ,primary key,secondary key etc. Also have others procedure like inner joint,outer joint etc. If you take a short course everything will be clear I think.