Monday, March 26, 2012

SQL Server 2008: Owners vs. Schemas

The other day someone asked me what is dbo, they had trouble differentiating between dbo as object owner and dbo as a schema. That conversation was what inspired this post.

Every object created in SQL Server must have an owner and most of the time the owner is dbo, which is the database owner. One can easily determine the owner of a particular database object by looking at the fully qualified name which is using the following convention:


Example: Server03.Northwind.dbo.Customers, where dbo is the owner of table Customers that belongs to Northwind database that resides on Server03.

Object gets its owner based on who created the object. By default the user account that creates the object will also own the object and only users in db_owner role can create objects owned by dbo. Someone in db_owner role can create an object owned by any user in the database. Only objects created by members of the sysadmin fixed server role (or by the dbo user) belong to dbo. Objects created by any other user who is not also a member of the sysadmin fixed server role (including members of the db_owner fixed database role):

•Belong to the user creating the object, not dbo.

•Are qualified with the name of the user who created the object.

A schema is a named container for database objects, which allows you to group objects into separate namespaces. It is basically a way to logically group objects such as tables, views, stored procedures etc.
You can assign a user login permissions to a single schema so that the user can only access the objects they are authorized to access. Schemas can be created and altered in a database, and users can be granted access to a schema. A schema can be owned by any user, and schema ownership is transferable.
The dbo schema is the default schema for a newly created database. The dbo schema is owned by the dbo user account. By default, users created with the CREATE USER Transact-SQL command have dbo as their default schema.

Users who are assigned the dbo schema do not inherit the permissions of the dbo user account. No permissions are inherited from a schema by users; schema permissions are inherited by the database objects contained in the schema.

Before SQL Server 2005, schemas used to be equivalent to database users. Now each schema is a distinct namespace that exists independently of the user who created it. It can be owned by any user and its ownership is transferable.

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