I am trying to build a multi user system and each user has different database.. is it possible in october cms.. So all the user access one login url.. So i don't need to install another fresh octobercms in the server..
I think you're referring to a Multitenancy.
You basically have two options :
a) Shared Database
b) Multi tenant Databases ( What you are asking )
Have a look at this laravel package to get an idea how to implement it but Keep in mind that building model relations across databases can be a pain and don't forget about future migrations ect..
The general idea here is (b) ;
If you're just playing around there's nothing wrong with it but I wouldn't recommend it for a commercial project unless you're experienced enough.
Having said that, If you want to proceed with option (a) all you need to do is add a tenant_id
field to all tables / relations and to all queries as a security precaution.