Enabling RLS on tables in Supabase - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does RLS stand for in database security?

RLS stands for Row-Level Security. It controls access to rows in a database table based on user permissions.

beginner

How do you enable RLS on a table in Supabase?

You enable RLS by running the SQL command: ALTER TABLE your_table ENABLE ROW LEVEL SECURITY;

intermediate

Why is it important to create policies after enabling RLS?

Because enabling RLS blocks all access by default. Policies define who can read or write rows, so without policies, no one can access the data.

intermediate

What is a simple example of a policy to allow users to select their own rows?

A policy like: CREATE POLICY "Users can select their rows" ON your_table FOR SELECT USING (auth.uid() = user_id); allows users to see only rows where their user ID matches.

beginner

What happens if you enable RLS but do not create any policies?

No one can access the table data because RLS blocks all access by default until policies are defined.

What is the first step to enable Row-Level Security on a table in Supabase?

A Insert data into the table

B Create a policy for the table

C Run <code>ALTER TABLE your_table ENABLE ROW LEVEL SECURITY;</code>

D Disable RLS on the table

You must first enable RLS on the table before creating policies.

After enabling RLS, what must you do to allow users to access data?

A Create policies that define access rules

B Disable RLS

C Grant admin rights to all users

D Nothing, access is automatic

Policies specify who can access which rows after RLS is enabled.

What does the policy condition auth.uid() = user_id do?

A Blocks all access

B Allows users to access only their own rows

C Allows all users to access all rows

D Allows access only to admins

It matches the authenticated user's ID to the user_id column to restrict access.

If RLS is enabled but no policies exist, who can access the table?

A No one

B Everyone

C Only admins

D Only the table owner

RLS blocks all access by default until policies are created.

Which SQL command disables RLS on a table?

A ALTER TABLE your_table ENABLE ROW LEVEL SECURITY;

B DROP POLICY ON your_table;

C CREATE POLICY ON your_table;

D ALTER TABLE your_table DISABLE ROW LEVEL SECURITY;

This command disables RLS on the specified table.

Explain the steps to enable Row-Level Security on a Supabase table and allow users to access only their own data.

Think about enabling RLS first, then defining who can see what.

Describe what happens to table access when RLS is enabled but no policies are defined.

Consider the default behavior of RLS.

Practice

1. What does enabling Row Level Security (RLS) on a Supabase table do?

easy

A. It backs up the table data to a secure location.

B. It encrypts the entire table data automatically.

C. It controls which rows a user can access based on their identity.

D. It increases the table's storage capacity.

Solution

1. Step 1: Understand RLS purpose

   RLS restricts access to rows in a table depending on who the user is.

2. Step 2: Compare options

   Only It controls which rows a user can access based on their identity. describes controlling row access by user identity, others describe unrelated features.

3. Final Answer:

   It controls which rows a user can access based on their identity. -> Option C

4. Quick Check:

   RLS = Row access control [OK]

Hint: RLS controls row access by user identity, not encryption or backup [OK]

Common Mistakes:

• Confusing RLS with encryption
• Thinking RLS backs up data
• Assuming RLS increases storage

2. Which SQL command correctly enables Row Level Security on a table named profiles in Supabase?

easy

A. ALTER TABLE profiles SET RLS = TRUE;

B. ALTER TABLE profiles ENABLE ROW LEVEL SECURITY;

C. ENABLE RLS ON TABLE profiles;

D. SET ROW LEVEL SECURITY ON profiles;

Solution

1. Step 1: Recall correct SQL syntax for enabling RLS

   The correct command is ALTER TABLE [table_name] ENABLE ROW LEVEL SECURITY;.

2. Step 2: Match options to syntax

   Only ALTER TABLE profiles ENABLE ROW LEVEL SECURITY; matches the exact syntax; others are invalid SQL commands.

3. Final Answer:

   ALTER TABLE profiles ENABLE ROW LEVEL SECURITY; -> Option B

4. Quick Check:

   ALTER TABLE + ENABLE ROW LEVEL SECURITY = correct syntax [OK]

Hint: Use ALTER TABLE ... ENABLE ROW LEVEL SECURITY to enable RLS [OK]

Common Mistakes:

• Using SET instead of ENABLE
• Wrong command order
• Missing ALTER TABLE keyword

3. Given the following policy on table tasks with RLS enabled:

CREATE POLICY "Users can view their tasks" ON tasks FOR SELECT USING (user_id = auth.uid());

What will happen if a user tries to select tasks where user_id is different from their own?

medium

A. They will see only tasks where user_id matches their auth.uid().

B. They will get a syntax error.

C. They will see all tasks regardless of user_id.

D. They will see no tasks at all.

Solution

1. Step 1: Understand the policy condition

   The policy allows SELECT only if user_id = auth.uid(), meaning users see only their own tasks.

2. Step 2: Predict query result for mismatched user_id

   If user_id differs, the condition fails, so those rows are not visible.

3. Final Answer:

   They will see only tasks where user_id matches their auth.uid(). -> Option A

4. Quick Check:

   Policy filters rows by user_id = auth.uid() [OK]

Hint: Policy USING clause filters rows by user identity [OK]

Common Mistakes:

• Assuming all rows are visible
• Expecting syntax errors from policy
• Thinking no rows are visible at all

4. You enabled RLS on the orders table but users report they cannot see any rows even though policies exist. What is the most likely cause?

medium

A. The table has too many rows.

B. The table is missing a primary key.

C. The database connection is lost.

D. RLS is enabled but no policies allow access to rows.

Solution

1. Step 1: Understand RLS behavior

   When RLS is enabled, access depends on policies. Without policies allowing access, no rows are visible.

2. Step 2: Evaluate other options

   Missing primary key, connection loss, or row count do not directly cause no rows to show due to RLS.

3. Final Answer:

   RLS is enabled but no policies allow access to rows. -> Option D

4. Quick Check:

   RLS needs policies to permit row access [OK]

Hint: Enable policies after RLS to allow row access [OK]

Common Mistakes:

• Ignoring missing policies
• Blaming unrelated database issues
• Assuming RLS shows all rows by default

5. You want to allow users to insert rows into the messages table only if the sender_id matches their authenticated user ID. Which policy correctly enforces this with RLS enabled?

hard

A. CREATE POLICY "Allow insert if sender matches" ON messages FOR INSERT WITH CHECK (sender_id = auth.uid());

B. CREATE POLICY "Allow insert" ON messages FOR INSERT USING (sender_id = auth.uid());

C. CREATE POLICY "Allow insert" ON messages FOR SELECT WITH CHECK (sender_id = auth.uid());

D. CREATE POLICY "Allow insert" ON messages FOR UPDATE WITH CHECK (sender_id = auth.uid());

Solution

1. Step 1: Identify correct policy type for INSERT

   For INSERT, WITH CHECK controls if new rows meet the condition.

2. Step 2: Match condition to sender_id and auth.uid()

   The condition sender_id = auth.uid() ensures users insert only their own messages.

3. Step 3: Verify options

   CREATE POLICY "Allow insert if sender matches" ON messages FOR INSERT WITH CHECK (sender_id = auth.uid()); uses FOR INSERT with WITH CHECK and correct condition; others use wrong commands or clauses.

4. Final Answer:

   CREATE POLICY "Allow insert if sender matches" ON messages FOR INSERT WITH CHECK (sender_id = auth.uid()); -> Option A

5. Quick Check:

   INSERT policies use WITH CHECK to validate new rows [OK]

Hint: Use WITH CHECK for INSERT policies to validate new rows [OK]

Common Mistakes:

• Using USING instead of WITH CHECK for INSERT
• Applying SELECT or UPDATE instead of INSERT
• Missing condition on sender_id