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In today’s world, data security is of paramount importance and as SQL developers, it’s crucial to know how to ensure data protection in your applications. One such technique is SQL Server Row-Level Security (RLS).
What is SQL Server Row-Level Security (RLS)?
SQL Server RLS is a feature that allows SQL Server to control access to rows in a database table based on the characteristics of the user executing a query (like identity, role, or membership).
Implementing SQL Server RLS
To implement the RLS in SQL Server, we will create Security Predicate function and a Security Policy.
1. Creating Security Predicate Function
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CREATE FUNCTION dbo.fn_securitypredicate(@EmpID AS sysname) RETURNS TABLE WITH SCHEMABINDING AS RETURN SELECT 1 AS fn_securitypredicate_result WHERE @EmpID = USER_NAME(); |
In this function, we are creating a predicate that will return ‘1’ if the passed in EmpID matches the current user. The function returns a table, which is required by the security policy.
2. Creating Security Policy
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CREATE SECURITY POLICY dbo.securityPolicy_emp ADD FILTER PREDICATE dbo.fn_securitypredicate(EmpID) ON dbo.Employees, ADD BLOCK PREDICATE dbo.fn_securitypredicate(EmpID) ON dbo.Employees WITH (STATE = ON); |
This security policy adds FILTER and BLOCK predicates to the Employees table. The filter predicate limits which rows can be returned in a SELECT operation, and the block predicate prevents insert, update, or delete operations that would change the EmpID to a value outside the allowed list.
Testing SQL Server RLS
Log on as a different user to test if the security policy is working as expected.
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EXECUTE AS USER = 'User1'; SELECT * FROM dbo.Employees; REVERT; |
In the above T-SQL code, we’re executing the query as ‘User1’. If the security policy works as expected, you should only see rows in the Employees table where the EmpID for ‘User1’ is present.
Conclusion
SQL Server Row-Level Security provides an effective way to restrict data access at the row level based on user characteristics. This not only enhances data security but also reduces the risk of accidental data manipulation. Remember, it’s crucial to test your security policies thoroughly to ensure they behave as expected.