Hi all

We have several site (6) and each of them has users. About a user we save personal information and login data (password).

Now, we are thinking to integrate all these sites, and to launch an umbrella site, which permits all users to acces all these sites. That means that from those 6 databases i have to extract the personal and login info and store in one place and rewrite all sites to use those tables for login and updating personal info.

These sites are on one dedicated server, so I thought of the following thing. A transition of several steps.
1. Standardising those fields that need to be stored in one place (pers data)
2. Separating from the rest of the tables (these data are stored differently in each database, sometimes in different tables)
3. Creating a database only for these data.

(all sites will still have their specific databases)

QUESTIONS:
1. What performance do i get when sometimes I have to make a query using 2 different databases. (Select database1.tablex.fieldy, database2.tablea.fieldb WHere ...)

2. Is there a better way?

We have arround 200.000 users on these 6 sites. (hopefully this number will grow)

Thanks