Because as Ivan said (this is assuming you want to migrate one or some of the sites not all) you would need to use a script like sed or manually separate the tables with the appropriate prefix from the rest of the databse. You might be able to export foo_% but I didn't think using the % variable worked on tables - I could be mistaken.
either way, that's just one of several reasons given why a single database can be more complicated and less desirable than separate databases - however no one said it can't be done and if the benefit outweighs the drawbacks mentioned you certainly can do it, just that there are reasons why it is not the best way to go.
Earnie Boyd wrote:
Quoting sander-martijn lists@severeddreams.com:
two more things: if you have a need to migrate one of the sites to it's own install at some point (because of high traffic for example) it would be a bigger job to migrate the database.
Why? You would just export the tables you need (E.G. foo_%), create the new DB and then import the tables. The settings.php file for the site would remain the same except for pointing to the new DB.
Earnie -- http://for-my-kids.com/ -- http://give-me-an-offer.com/