performance effect of joining tables form different databases

Question

I have a web site using a database named lets say "site1". I am planning to put another site on the same server which will also use some of the tables from "site1".

So should I use three different databases like "site1" (for first site specific data), "site2" (for second site specific data), and "general" (for common tables). In which there will be join statements between databases general and site1 and site2. Or should I put all tables in one database?

Which is the best practice to do? How performances differ in each situation? I am using MySQL. So how is the situation especially for MySQL?

Thanks in advance...

Answer 1

I believe it can be done but i'm not sure about the performance implications. Take a look at these links:

• http://stackoverflow.com/questions/1675333/php-mysql-joins-across-databases
• http://www.shawnhogan.com/2005/12/cross-database-join-with-mysql.html

I'll look around some more to see if I can find more info on performance.

This link seems to suggest there isn't a significant performance hit.