SQL Server Developer: Permissions

This section delves into the intricate world of permissions within SQL Server, a critical aspect of database security that governs what actions users and applications can perform on database objects.

Understanding Database Permissions

Permissions in SQL Server are the foundation of the principle of least privilege. They define the access rights granted to logins, users, roles, and application roles, ensuring that only authorized entities can interact with sensitive data and perform specific operations.

Key Concepts:

  • Principals: These are entities that can be granted permissions, including server-level logins and database-level users.
  • Securables: These are the objects or actions that permissions can be applied to, such as tables, views, stored procedures, schemas, databases, and even server-level tasks.
  • Permissions: The specific actions that a principal is allowed or denied to perform on a securable. Common permissions include SELECT, INSERT, UPDATE, DELETE, EXECUTE, and CONTROL.

Best Practice: Always grant the minimum set of permissions necessary for a user or application to perform its intended tasks. Avoid granting broad permissions like db_owner unless absolutely required.

Managing Permissions

SQL Server provides several ways to manage permissions:

1. GRANT, DENY, REVOKE Statements

These Transact-SQL statements are the fundamental commands for managing permissions directly.

  • GRANT: Used to grant a permission to a principal.
  • DENY: Used to explicitly deny a permission. Deny statements take precedence over Grant statements.
  • REVOKE: Used to remove a previously granted or denied permission.

Example: Granting SELECT permission on a table


GRANT SELECT ON dbo.Customers TO AppUser;

Example: Denying DELETE permission on a table


DENY DELETE ON dbo.Orders TO ReportUser;

Example: Revoking SELECT permission


REVOKE SELECT ON dbo.Products TO GuestUser;

2. Database Roles

Database roles are collections of permissions that can be assigned to users, simplifying management. SQL Server provides several fixed database roles, and you can create custom roles for more granular control.

  • Fixed Database Roles: Such as db_datareader, db_datawriter, db_ddladmin, and db_owner.
  • User-Defined Roles: Created to group specific sets of permissions for custom application needs.

Security Tip: Using roles is generally preferred over assigning permissions directly to individual users. This makes it easier to manage permissions when users join or leave teams, or when application requirements change.

3. Stored Procedures and Functions

You can control access to stored procedures and functions using the EXECUTE permission. This allows you to encapsulate complex logic and expose only specific functionalities to users.

4. Schemas

Schemas provide a way to group database objects and manage permissions at a higher level. By assigning users to specific schemas, you can control their access to all objects within that schema.

Permission Levels

Permissions can be applied at various levels:

  • Server Level: Permissions related to the SQL Server instance itself (e.g., ALTER ANY LOGIN).
  • Database Level: Permissions that apply to the entire database (e.g., CREATE TABLE).
  • Schema Level: Permissions that apply to all objects within a schema.
  • Object Level: Permissions on specific objects like tables, views, or stored procedures.

Common Security Scenarios

  • Read-Only Users: Grant SELECT permission on necessary tables and views, or assign to db_datareader role.
  • Data Entry Users: Grant SELECT, INSERT, and UPDATE permissions on specific tables.
  • Application Service Accounts: Grant minimal permissions required for the application to function, often including EXECUTE on specific stored procedures and SELECT, INSERT, UPDATE on tables.
  • Administrative Users: Grant broader permissions, but use roles like db_owner or custom administrative roles with caution.

Further Reading