August, 2011

A common scenario in data warehousing applications is knowing what source system records to update, what data needs to be loaded and which data rows can be skipped as nothing has changed since they were last loaded. Another possible scenario is the need to facilitate searching data that is encrypted using cell level encryption or storing application passwords inside the database.

 Data Hashing can be used to solve this problem in SQL Server.

 A hash is a number that is generated by reading the contents of a document or message. Different messages should generate different hash values, but the same message causes the algorithm to generate the same hash value.

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Don Pinto, PM, SQL Server Engine

I am posting this on behalf of my colleague Rick Byham, a technical writer on the SQL Server Team.

Database Engine permissions are managed at the server level through logins and fixed server roles, and at the database level through database users and user-defined database roles.

Logins

Logins are individual user accounts for logging on to the SQL Server Database Engine. SQL Server supports logins based on Windows authentication and logins based on SQL Server authentication. For information about the two types of logins, see Choosing an Authentication Mode .

Fixed Server Roles

Fixed server roles are a set of preconfigured roles that provide convenient group of server-level permissions. Logins can be added to the roles using the sp_addsrvrolemember procedure.

Database Users

Logins are granted access to a database by creating a database user in a database and mapping that database user to login. Typically the database user name is the same as the login name, though it does not have to be the same. Each database user maps to a single login. A login can be mapped to only one user in a database, but can be mapped as a database user in several different databases.

Fixed Database Roles

Fixed database roles are a set of preconfigured roles that provide convenient group of database-level permissions. Database users and user-defined database roles can be added to the fixed database roles using the sp_addrolemember procedure.

User-defined Database Roles

Users with the CREATE ROLE permission can create new user-defined database roles to represent groups of users with common permissions. Typically permissions are granted or denied to the entire role, simplifying permissions management and monitoring.

Typical Scenario

The following example represents a common and recommended method of configuring permissions.

In Active Directory:

1. Create a Windows user for each person.
2. Create Windows groups that represent the work units and the work functions.
3. Add the Windows users to the Windows groups.

In SQL Server:

1. Create a login for the Windows groups. (If using SQL Server authentication, skip the Active Directory steps, and create SQL Server authentication logins here.)
2. Create a database user for the login representing the Windows groups.
3. Create one or more user-defined database roles, each representing a similar function. For example financial analyst, and sales analyst.
4. Add database users to one or more user-defined database roles.
5. Grant permissions to the user-defined database roles.

Assigning Permissions

Most permission statements have the format :

AUTHORIZATION PERMISSION ON SECURABLE::NAME TO PRINCIPAL

• AUTHORIZATION must be GRANT, REVOKE or DENY.
• PERMISSION is listed in the chart referenced below.
• ON SECURABLE::NAME is the server, server object, database, or database object and its name. Some permissions do not require ON SECURABLE::NAME because it is unambiguous or inappropriate in the context. For example the CREATE TABLE permission doesn’t require the ON SECURABLE::NAME clause.
• PRINCIPAL is the login, user, or role which receives or loses the permission. Grant permissions to roles whenever possible.

Sample grant statement: GRANT UPDATE ON OBJECT::Production.Parts TO PartsTeam

Permissions are granted to security principals (logins, users, and roles) by using the GRANT statement. Permissions are explicitly denied by using the DENY command. A previously granted or denied permission is removed by using the REVOKE statement. Permissions are cumulative, with the user receiving all the permissions granted to the user, login, and any group memberships; however any permission denial overrides all grants.

Tip: A common mistake is to attempt to remove a GRANT by using DENY instead of REVOKE. This can cause problems when a user receives permissions from multiple sources; which is quite common. The following example demonstrates the principal.

The Sales group receives SELECT permissions on the OrderStatus table through the statement GRANT SELECT ON OBJECT::OrderStatus TO Sales. User Ted is a member of the Sales role. Ted has also been granted SELECT permission to the OrderStatus table under his own user name through the statement GRANT SELECT ON OBJECT::OrderStatus TO Ted. Presume the administer wishes to remove the GRANT to the Sales role.

• If the administrator correctly executes REVOKE SELECT ON OBJECT::OrderStatus TO Sales, then Ted will retain SELECT access to the OrderStatus table through his individual GRANT statement.
• If the administrator incorrectly executes DENY SELECT ON OBJECT::OrderStatus TO Sales then Ted, as a member of the Sales role, will be denied the SELECT permission because the DENY to Sales overrides his individual GRANT.

Permission Hierarchy

Permissions have a parent/child hierarchy. That is, if you grant SELECT permission on a database, if includes SELECT permission on all (child) schemas in the database. If you grant SELECT permission on a schema, it includes SELECT permission on all the (child) tables and views in the schema. The permissions are transitive; that is, if you grant SELECT permission on a database, it includes SELECT permission on all (child) schemas, and all (grandchild) tables, and all views.

Permissions also have covering permissions. The CONTROL permission on an object, normally gives you all other permissions on the object.

Because both the parent/child hierarchy and the covering hierarchy can act on the same permission, the permission system can get complicated. For example, let's take a table (Region), in a schema (Customers), in a database (SalesDB).

• CONTROL permission on table Region includes all the other permissions on the table Region, including ALTER, SELECT, INSERT, UPDATE, DELETE, and some other permissions.
• SELECT on the Customers schema that owns the Region table includes the SELECT permission on the Region table.

So SELECT permission on the Region table can be achieved through any of these three statements:

• GRANT SELECT ON OBJECT::Region TO Ted
• GRANT CONTROL ON OBJECT::Region TO Ted
• GRANT SELECT ON SCHEMA::Customers TO Ted
• GRANT CONTROL ON SCHEMA::Customers TO Ted
• GRANT SELECT ON DATABASE::SalesDB TO Ted
• GRANT CONTROL ON DATABASE::SalesDB TO Ted

Grant the Least Permissions

The first permission listed above (GRANT SELECT ON OBJECT::Region TO Ted) is the most granular, that is, that statement is the least permission possible that grants the SELECT. No permissions to subordinate objects come with it. Always grant the least permission possible, but grant at higher levels in order to simplify the granting system. So if Ted needs permissions to the entire schema, grant SELECT once at the schema level, instead of granting SELECT at the table of view level many times. The design of the database has a great deal of impact on how successful this strategy can be. This strategy will work best when your database is designed so that objects needing identical permissions are included in a single schema.

List of Permissions

SQL Server 2008 R2 has 195 permissions. SQL Server Code-named 'Denali' has 214 permissions. The following graphic shows the permissions and their relationships to each other. Some of the higher level permissions (such as CONTROL SERVER) are listed many times.
5710.Permissions_Poster_2008_R2_Wiki.pdf

Permissions vs. Fixed Server and Fixed Database Roles

The permissions of the fixed server roles and fixed database roles are similar but not exactly the same as the granular permissions. For example, members of the sysadmin fixed server role have all permissions on the instance of SQL Server, as do logins with the CONTROL SERVER permission. But granting the CONTROL SERVER permission does not make a login a member of the sysadmin fixed server role, and making adding a login to the sysadmin fixed server role does not explicitly grant the login the CONTROL SERVER permission. Sometimes a stored procedure will check permissions by checking the fixed role and not checking the granular permission. For example detaching a database requires membership in the db_owner fixed database role. The equivalent CONTROL DATABASE permission is not enough. These two systems operate in parallel but rarely interact with each other. Microsoft recommends using the newer, granular permission system instead of the fixed roles whenever possible.

Monitoring permissions

The following views return security information.

• The logins and user-defined server roles (available in SQL Server Code-named 'Denali') on a server can be examined by using the sys.server_principals view.
• The users and user-defined roles in a database can be examined by using the sys.database_principals view.
• The permissions granted to logins and user-defined fixed server roles can be examined by using the sys.server_permissions view.
• The permissions granted to user and user-defined fixed database roles can be examined by using the sys.database_permissions view.
• Database role membership can be examined by using the sys. sys.database_role_members view.
• Server role membership can be examined by using the sys. sys.server_role_members view.
• For additional security related views, see Security Catalog Views (Transact-SQL) .

The following statements return useful information about permissions.

To return the explicit permissions granted or denied in a database, execute the following statement in the database.

SELECT
perms.state_desc AS State,
permission_name AS [Permission],
obj.name AS [on Object],
dPrinc.name AS [to User Name],
sPrinc.name AS [who is Login Name]
FROM sys.database_permissions AS perms
JOIN sys.database_principals AS dPrinc
ON perms.grantee_principal_id = dPrinc.principal_id
JOIN sys.objects AS obj
ON perms.major_id = obj.object_id
LEFT OUTER JOIN sys.server_principals AS sPrinc
ON dPrinc.sid = sPrinc.sid

To return the members of the server roles, execute the following statement.

SELECT sRole.name AS [Server Role Name] , sPrinc.name AS [Members]
FROM sys.server_role_members AS sRo
JOIN sys.server_principals AS sPrinc
ON sRo.member_principal_id = sPrinc.principal_id
JOIN sys.server_principals AS sRole
ON sRo.role_principal_id = sRole.principal_id;

To return the members of the database roles, execute the following statement in the database.

SELECT dRole.name AS [Database Role Name], dPrinc.name AS [Members]
FROM sys.database_role_members AS dRo
JOIN sys.database_principals AS dPrinc
ON dRo.member_principal_id = dPrinc.principal_id
JOIN sys.database_principals AS dRole
ON dRo.role_principal_id = dRole.principal_id;