Do you mean, 1 server, 3 sites and 3 prefixes? If yes, all scripts use the same username and password. They will read information from the same database. It's the task of the script to read only the tables with the prefixes he knows (the one you set-up when you installed the scripts).
the prefix and are not same ,the frist one let say is red and #2 say brown and also the table r not one say username and #2 say usr_alias but r in the same datebase
Lamont, You can share a database across multiple applications, etc. You stated that there are three prefixes, so I am going to assume that you entered a different prefix during three separate application installations. Correct? If this is correct, then you should have entered the database connection information too. The host name should point to the same instance and the username and passwords as needed. Also, are the sites on the same host? Give me exact details and I will help out. Social.Network