Database / Supabase basics Interview Questions

Define Row Level Security in Supabase?

Row Level Security (RLS) is a native PostgreSQL feature that restricts which rows a given database role can see or modify, enforced by the database engine itself rather than by application code. Supabase turns this into its primary authorization model.

Because RLS runs inside Postgres, it holds even if a client bypasses your app and calls the auto-generated API directly — a policy such as "users can only select rows where user_id = auth.uid()" is checked on every query, not just ones your frontend happens to write correctly.

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Where is a Row Level Security policy actually enforced? In the browser's local storage

✗ Try again, that's not it.

In the DNS layer

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Inside the Postgres database engine

✓ Correct! Well done.

In the React frontend

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Why does RLS remain effective even if a client calls the API directly, bypassing your app's UI? Because it encrypts the whole database

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Because it's checked by Postgres on every query, not by the frontend

✓ Correct! Well done.

Because the API is IP-restricted

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Because RLS disables the API entirely

✗ Try again, that's not it.

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More Related questions...

What is Supabase? What is the purpose of PostgreSQL within Supabase? What are the core services offered by Supabase? What is Supabase Authentication used for? What are the types of storage available in Supabase Storage? Define Row Level Security in Supabase? Describe the Supabase client library? What is the purpose of Supabase Edge Functions? List the API types Supabase auto-generates from your schema? How do you create a new Supabase project and connect to it? How does Supabase auto-generate REST APIs from a database schema? Why is Row Level Security important in a client-facing Supabase app? How does Supabase Realtime broadcast database changes to clients? What is the difference between the anon key and the service role key in Supabase? When should you use an Edge Function instead of a Postgres database function? How do you troubleshoot a valid query being blocked by Row Level Security? What is the difference between using Supabase Auth and rolling your own JWT-based authentication? How is data validated before insertion in a Supabase table? Why do we use database migrations in Supabase projects? What happens when a Postgres trigger fires on a table linked to Edge Function webhooks? Explain the execution flow of a request through Supabase's auto-generated API? Why doesn't Supabase recommend using the service_role key on the client? How can you optimize Postgres connection pooling for serverless Edge Functions? Explain the internal working of Row Level Security policy evaluation in Postgres? What is the difference between pgvector similarity search and hybrid search in Supabase? Which is better for real-time collaboration, Supabase Realtime or client-side polling, and why? How does Supabase handle connection pooling for high-concurrency workloads? Explain the lifecycle of a Supabase Auth session token? When would you choose self-hosting Supabase over the managed cloud offering? How do you optimize full-text search performance on a large Postgres table in Supabase?

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Database / Supabase basics Interview Questions

Define Row Level Security in Supabase?

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