PostgreSQL Row-Level Security Explained: From Basics to Best Practices

In a multi-tenant or secure data environment, it's not enough to just control who can access a table. You often need to control which rows within that table each user can access. This is where PostgreSQL’s powerful Row-Level Security (RLS) comes into play.

In this guide, we’ll walk through what RLS is, why you’d use it, and how to implement it securely and effectively.

🔐 What is Row-Level Security?

Row-Level Security allows you to restrict data access at the level of individual rows. When enabled, PostgreSQL will evaluate a policy for every query—`SELECT`, `INSERT`, `UPDATE`, or `DELETE`—to determine if a user has permission to see or modify each row.

📈 Use Cases:

• Multi-tenant SaaS applications: Ensure users only access their own organization's data

• Regulatory compliance: Enforce data visibility based on user roles or geography

• Fine-grained auditing and tracking

🧱 Step-by-Step Implementation

Step 1: Create a Sample Table

CREATE TABLE documents (
	id SERIAL PRIMARY KEY,
	content TEXT,
	owner TEXT  -- This can be username or tenant ID
);

Step 2: Add Some Sample Data

INSERT INTO documents (content, owner) VALUES
('Confidential Project A', 'john'),
('Confidential Report B', 'julie');

Step 3: Create Roles

CREATE ROLE john LOGIN;
CREATE ROLE julie LOGIN;

Step 4: Enable Row-Level Security

ALTER TABLE documents ENABLE ROW LEVEL SECURITY;

Step 5: Define Policies

CREATE POLICY docs_select_policy
	ON documents
	FOR SELECT
	USING (owner = current_user);

You can define additional policies for INSERT, UPDATE, or DELETE:

Example:

CREATE POLICY docs_insert_policy
ON documents
FOR INSERT
WITH CHECK (owner = current_user);

Step 6: Grant Permissions

GRANT SELECT, INSERT ON documents TO john, julie;

Now, when Julie logs in, she’ll only see her documents:

SET SESSION AUTHORIZATION julie;
SELECT * FROM documents;
-- Returns only rows where owner = 'julie'

🧪 Troubleshooting: Why Am I Not Seeing Any Rows?

If no rows are returned for a user even though data exists, use this checklist:

✅ 1. Verify RLS is Enabled

ALTER TABLE documents ENABLE ROW LEVEL SECURITY;

✅ 2. Confirm the SELECT Policy Exists

SELECT * FROM pg_policies WHERE tablename = 'documents';

✅ 3. Confirm Role Permissions

GRANT SELECT ON documents TO julie;

✅ 4. Check Data Consistency

SELECT DISTINCT owner FROM documents;
-- Ensure 'julie' matches exactly (case-sensitive)

✅ 5. Confirm Role Context

SET SESSION AUTHORIZATION julie;
SELECT current_user;
SELECT * FROM documents;

✅ 6. Debug with Explicit Check

SELECT *, current_user = owner AS allowed FROM documents;

This shows which rows pass the RLS policy for the current user.

✅ Best Practices

• Least privilege: Use RLS alongside traditional GRANT/REVOKE permissions

• Avoid leaking metadata: Don’t allow unrestricted access to primary keys or counts

• Audit policies: Document and test all policies thoroughly

• Use SECURITY DEFINER functions cautiously** if bypassing RLS is required

🚨 Common Pitfalls to Avoid

• Policies must be explicitly defined for each operation (SELECT, INSERT, etc.)

• Superusers bypass RLS entirely

• If no policies are defined, access is denied by default (secure-by-default)

🧩 Advanced Tips

• Use current_setting() to pass app-level context into queries

• Combine RLS with PostgreSQL views for even tighter abstraction

🧭 Conclusion

Row-Level Security in PostgreSQL is a powerful feature that, when implemented carefully, can dramatically increase the security and flexibility of your application’s data model. It’s especially useful in multi-tenant architectures and environments with strict data access policies.