copy database for duplicate site?
You can simply copy database all right, if you remember about critical points:


Make sure settings.php really points to proper databases
Before importing SQL file to new database, find and replace old URL and site name with new one.
If you keep any cache settings for external tools, like memcached, in database, make sure you either uninstall them before SQL export and then install again, or find &amp; replace in SQL file before importing.