Row-level Security (RLS) is a feature in Microsoft Azure SQL that allows administrators to control which users can access data in a table based on the property values of the data. With RLS, you can implement restrictions on data row access. For instance, you can ensure that workers can access only those data rows that pertain to their department.
This feature simplifies the design and coding of security in your application and enhances your database’s overall security health since RLS encapsulates the access restriction logic within the database tier itself, rather than away from the data.
How does Row-Level Security work?
RLS works by implementing a function, known as a “security predicate”, that gets applied to all SELECT, UPDATE, DELETE, and INSERT statements that users execute on the table. This function specifies who does or does not have permission to access a given data row.
Following are the key terms you need to understand in RLS:
- Security Predicate: A function that filters out rows that do not meet the security criteria.
- Security Policy: A database object that links a security predicate to a table or view.
- Schema-bound inline table-valued function(ITVF): A function to implement the security predicate.
Implementing Row-Level Security
Here is an example to illustrate how to implement Row-Level Security. In this example, we will be applying RLS to a table named ‘SalesOrder’. What we are trying to achieve is that a salesperson can only see their own sales order data.
- The first step is to create a Schema-bound inline table-valued function(ITVF). This predicate function will define the filter that limits row visibility within the table.
CREATE FUNCTION Security.fn_securitypredicate(@SalesPersonID AS sysname)
RETURNS TABLE
WITH SCHEMABINDING
AS
RETURN SELECT 1 AS fn_securitypredicate_result
WHERE DATABASE_PRINCIPAL_ID() = ISNULL(DATABASE_PRINCIPAL_ID(@SalesPersonID), 0)
- After creating our predicate function, we need to create a security policy that will add this function to our ‘SalesOrder’ table:
CREATE SECURITY POLICY Security.SalesOrderPolicy
ADD FILTER PREDICATE Security.fn_securitypredicate(SalesPersonID)
ON dbo.SalesOrder,
ADD BLOCK PREDICATE Security.fn_securitypredicate(SalesPersonID)
ON dbo.SalesOrder
With the creation of the security policy, our Row-Level Security implementation is complete. Now, when a salesman runs a query on the ‘SalesOrder’ table, he will only see the rows related to his sales.
Row-level security provides a more secure and easy way of data control in a granular size. It is a potent tool when leveraged correctly, but as always, it requires careful planning and testing to ensure it aligns with your organization’s security requirements. Regular audits of security policies can help ensure the filters and blocks are working as expected.
In the DP-300 Administering Microsoft Azure SQL Solutions exam, understanding how to implement row-level security is pivotal, as it assists in managing comprehensive security capabilities efficiently at both the server and database levels.
Practice Test
True or False: Row-level security (RLS) enables you to restrict data access at the row level based on the user’s identity, role, or membership.
Answer: True
Explanation: Row-level security (RLS) allows you to control access to rows in a database table based on the characteristics of the user.
In SQL Server, Row-level security:
- a) Is at the database level
- b) Is at the table level
- c) Is on the application side
- d) None of the above
Answer: b) Is at the table level
Explanation: Row-Level Security enables you to restrict read and write access to rows in a database table at the table level.
True or False: Row-Level Security can be implemented by using a security policy.
Answer: True
Explanation: Security Policy is a term used in SQL Server programming to implement Row-Level Security.
Which of these are necessary to implement Row-Level Security in SQL Server?
- a) Security Predicate
- b) Security Policy
- c) User Role
- d) All of the above
Answer: d) All of the above
Explanation: Implementing Row-Level Security in SQL Server requires creating a Security Predicate, applying a Security Policy, and assigning User Roles.
True or False: In Row-Level Security, users can access data in the table that the DBA has not granted them permission to see.
Answer: False
Explanation: Row-Level Security restricts data access at the row level based on permissions, users cannot view data that they do not have access to.
Which of these statements is true about implementing row-level security in Azure SQL Database?
- a) It requires major application changes
- b) It requires no application changes
- c) It requires some application changes
- d) None of the above
Answer: b) It requires no application changes
Explanation: Implementing row-level security in Azure SQL Database can be done transparently and does not require changes to the application.
Which type of security function filters rows in table and doesn’t allow the users to view data they are not supposed to see?
- a) Predicate function
- b) Inline function
- c) Security function
- d) None of the above
Answer: a) Predicate function
Explanation: The filter predicate function filters the rows in a table and hence, users cannot view the data they are not supposed to see.
True or False: A security policy that implements Row-Level Security in SQL Server requires at least one filter predicate or block predicate, or both.
Answer: True
Explanation: Security policy in SQL Server that implements RLS requires either filter predicate, block predicate or both to limit the rows that can be accessed.
Which of these is not a step in implementing row-level security?
- a) Create a security predicate
- b) Apply a filter
- c) Implement a security policy
- d) Create a database cluster
Answer: d) Create a database cluster
Explanation: Creating a database cluster is not a step in implementing row-level security. The steps generally involve creating a security predicate, applying a filter, and implementing a security policy.
True or False: In Row-Level Security, a function that specifies the exact rows to update or delete is a block predicate.
Answer: True
Explanation: In Row-Level Security, block predicates control the exact rows that can be updated or deleted by the user.
Is it necessary to use a scalar-valued function in row-level security?
- a) True
- b) False
Answer: a) True
Explanation: A scalar-valued function is necessary in RLS. It determines whether access to certain rows in a table is granted or denied.
What does the Transact-SQL statement “CREATE SECURITY POLICY” do?
- a) It creates a new security policy in the database
- b) It deletes an existing security policy from the database
- c) It changes an existing security policy in the database
- d) None of the above
Answer: a) It creates a new security policy in the database
Explanation: The “CREATE SECURITY POLICY” statement is used to create a new security policy in the SQL Server database for implementing row-level security.
True or False: Row-Level Security supports both on-premises SQL Server and Azure SQL Database.
Answer: True
Explanation: Row-Level Security is a feature supported by both on-premises SQL Server and Azure SQL Database.
Which of the following functions implements the logic to restrict data access at the row level?
- a) Security Predicate Function
- b) Implementation Predicate Function
- c) Logic Predicate Function
- d) None of the above
Answer: a) Security Predicate Function
Explanation: The Security Predicate Function is used to implement the logic that determines if a user has access to a specific row of data.
True or False: You can use the “ALTER SECURITY POLICY” statement to modify an existing security policy in SQL Server.
Answer: True
Explanation: The “ALTER SECURITY POLICY” statement is used to modify or change an existing security policy in SQL Server.
Interview Questions
What is row-level security in SQL?
Row-level security in SQL refers to restricting data that users view and interact with based on their access rights or roles. This is implemented through security predicates, mainly filter predicates and block predicates.
In SQL, what is a security predicate?
A security predicate in SQL is a function created by the database owner. Its role is to restrict the rows returned to a user, in line with the implemented row-level security strategy.
What are filter predicates in SQL?
Filter predicates are used in SQL to limit the rows visible in the result set of a query. It is a function used to narrow down data that users can select from a table.
What are block predicates in SQL?
Block predicates prevent users from performing certain actions on rows that violate a certain predicate function. These actions may include after insert, before insert, after update, before update among others.
How do you implement row-level security in Azure SQL?
Row-level security in Azure SQL is implemented by creating a security policy which includes creating a security predicate function and then adding the security policy to the database schema.
What is an inline table-valued function in the context of implementing row-level security in Azure SQL?
An inline table-valued function is created to determine the rows that the user is allowed to access. This function is then used in the security policy to implement row-level security.
Can row-level security be applied to views in Azure SQL?
No, row-level security cannot be directly applied to views in Azure SQL. It can only be implemented on tables.
What is the impact of applying multiple security policies to the same table in Azure SQL?
Multiple security policies applied on the same table in Azure SQL are combined using an AND operator. This means the user must meet all conditions specified in all the security policies to gain access.
What level of grant or rights is required to alter the security policy in Azure SQL?
ALTER permissions on the schema where the security policy exists is required to alter the security policy in Azure SQL.
How can one control access to data within a database in Azure SQL Database?
Access to data within a database in Azure SQL Database can be controlled by implementing row-level security, using authentication and authorization, access control, and encryption.
How does row-level security affect performance in Azure SQL Database?
The implementation of row-level security in Azure SQL Database usually has a minimal impact on performance. However, complex filtering logic can slow down data retrieval.
Can the database owner bypass the row-level security in Azure SQL Database?
No, the database owner cannot bypass the row-level security in Azure SQL Database. The security applies to all users, including the database owner and high privilege roles.
What command do you use to create a security policy in SQL?
The CREATE SECURITY POLICY command is used to create a security policy in SQL.
Can you disable row-level security in Azure SQL Database?
Yes, row-level security can be disabled in Azure SQL Database by using the ALTER SECURITY POLICY Transact-SQL command and setting the state option to OFF.
Can row-level security in Azure SQL Database distinguish between read and write operations?
Yes, the implementation of row-level security distinguishes between read and write operations as the policy uses different predicates (filter and block) to control these operations.