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Lets say I have two separate databases, X and Y, on the same physical server. All of my queries currently run out of X. I find I have one table in Y I would like to be available to X for JOINS. So... now I keep a copy of the one table I need for both X and Y in both X and Y, but the data in Y is constantly changing, so the copy soon becomes out of date. Not critical for this application, but for another I'm designing now this just won't do. X right now only needs read access to the table in Y. Is there an efficient way to do joins across the two databases? I'd prefer a mysql solution as opposed to opening multiple database connections in php. Thank you. EDIT: So what becomes of these lines?: $conn = mysql_connect('localhost','username','password'); @mysql_select_db('database_name',$conn) And yes.. this is an old app, hence the mysql instead of mysqli. Suppose I could convert it. EDIT2: So where I don't specify database_name.table_name and just specify table_name I get whatever is selected, and where I do specify database.table_name I get what I asked for.. right? Yep. Works. EDIT3: Is there any significant performance hit by doing cross database joins versus joins within the same database? Nope. Looks just as fast. Thank you all for your responses.

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