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Database / Supabase basics Interview Questions

Why is Row Level Security important in a client-facing Supabase app?

In a typical Supabase app, the frontend talks to the database almost directly through the auto-generated API using a public anon key that ships inside the client bundle. Without RLS, that key alone would be enough for anyone to read or modify every row in every table.

RLS closes that gap by moving authorization into the database itself: a policy checks conditions like auth.uid() = user_id on every row before returning or writing it, regardless of which client or tool issued the request. This is different from a traditional backend, where a private server sits between the client and the database and enforces access control in application code; Supabase's model instead assumes the API is public-facing and pushes the trust boundary down to Postgres.

Skipping RLS on a table that should be restricted is one of the most common Supabase security mistakes, since the table remains fully open to any authenticated (or even anonymous) client by default once RLS is off.

Why is the anon key alone not a sufficient security boundary in Supabase?
What happens to a table if RLS is left disabled?

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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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Supabase Intermediate to Advanced Interview Questions

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