Originally Posted by Varius

Will it be on the same server? If so, you can have different databases and access them without opening new connections. Cross-database joins also work fine in mysql.

Example:

you create three databases: common, site1, site2

You can do queries such as:

SELECT a.field1, a.field2, b.field2 FROM site1.table1 a JOIN common.table1 b ON a.field1=b.field1;

Basically, in your queries that use more than one database just have the dbname in the query before the table name.

Hope that answers your question.