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In today’s data-driven world, maintaining database security is paramount. One of the advanced security measures provided by SQL Server is Row-Level Security (RLS), which allows access control on a per-row basis. This tutorial will guide you on how to implement RLS using SQL.
What is Row-Level Security?
Row-Level Security introduces a security layer within the data access level of a database system. With RLS, database administrators can restrict data access at the row level based on user permission, roles, or claims. This makes it seamless to control which users can view or edit a row in a shared database table.
Implementing Row-Level Security in SQL Server
To implement RLS, the following steps are undertaken:
- Create a security predicate function
- Create a security policy and bind it with the function
1. Creating the Security Predicate Function
The security predicate function takes a table’s unique id and a user claim as inputs, then returns a boolean to indicate if the row can be accessed or not.
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CREATE FUNCTION Security.fn_securitypredicate(@PersonID AS int) RETURNS TABLE WITH SCHEMABINDING AS RETURN SELECT 1 AS fn_securitypredicate_result FROM Security.Users AS U WHERE U.UserName = USER_NAME() AND U.PersonID = @PersonID; |
2. Creating the Security Policy and Binding It
Once we have the security function in place, create a security policy and associate it with the function.
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CREATE SECURITY POLICY Security.EmployeesPolicy ADD FILTER PREDICATE Security.fn_securitypredicate(PersonID) ON HumanResources.Employee, ADD BLOCK PREDICATE Security.fn_securitypredicate(PersonID) ON HumanResources.Employee WITH (STATE = ON); |
Test SQL Server Row-Level security
With the security policy and function in place, you can now restrict or allow data access to different users of the SQL server. For instance, you can create a test user and validate the RLS implementation.
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CREATE USER TestUser WITHOUT LOGIN; GRANT SELECT ON HumanResources.Employee TO TestUser; EXECUTE AS USER = 'TestUser'; SELECT * FROM HumanResources.Employee; REVERT; |
Conclusion
Row-Level Security (RLS) is a powerful security feature in SQL Server that allows fine-grained access control on a per-row basis. However, it should be implemented and used wisely because misuse can lead to severe security holes. Remember, RLS complements other security measures and is not a replacement for them.