Contained databases are new in 2012 and we can define as "A contained database is a database that is isolated from other databases and from the instance of SQL Server that hosts the database."
SQL Server 2012 helps user to isolate their database from the instance in 4 ways.
1- Much of the metadata that describes a database is maintained in the database. (In addition to, or instead of, maintaining metadata in the master database.)
2- All metadata are defined using the same collation.
3- User authentication can be performed by the database, reducing the databases dependency on the logins of the instance of SQL Server.
4- The SQL Server environment (DMV's, XEvents, etc.) reports and can act upon containment information.
The following terms apply to the contained database model.
The boundary between a database and the instance of SQL Server. The boundary between a database and other databases.
An element that exists entirely in the database boundary.
An element that crosses the database boundary.
A database that has containment set to NONE. All databases in versions earlier than SQL Server 2012 are non-contained. By default, all SQL Server 2012 databases have a containment set to NONE.
Partially contained database
A partially contained database is a contained database that can allow some features that cross the database boundary. SQL Server includes the ability to determine when the containment boundary is crossed.
There are two types of users for contained databases.
· Contained database user with password
Contained database users with passwords are authenticated by the database.
· Windows principals
Authorized Windows users and members of authorized Windows groups can connect directly to the database and do not need logins in the master database. The database trusts the authentication by Windows.
Enabling contained database support from server properties
XEC sp_configure 'show advanced', 1
EXEC sp_configure 'contained database authentication', 1
Set option to Partial
Some features of partially contained databases, such as storing metadata in the database, apply to all SQL Server 2012 databases. Some benefits of partially contained databases, such as database level authentication and catalog collation, must be enabled before they are available
Creating a user that has no access outside its database is contained database user
User can create User, database role, application role, schema and audit specification for only one database and it runs within this database. Migrating of this database to other place only needs to backup and restore and you do not need to migrate users and other options with it.
You can create multiple types of users
Creating user with password to reside in local database
Assigning proper database rights, for admin user, it can only be access this database and perform all tasks.
Connecting to a contained database
You need to mention database name before connected to contained database
And you will only get your database. This is the best case for testing on production machine before deployment.