Database / Supabase Intermediate to Advanced Interview Questions

What is the difference between linking an OAuth identity and creating a brand-new user account?

Creating a brand-new account always produces a fresh row in auth.users with a new, unique user ID and no history. Linking an OAuth identity instead attaches a new sign-in method (say, Google) to an existing user row — the same user ID, same existing data, just an additional way to authenticate as that same person.

This distinction matters for account consolidation: if a user originally signed up with email/password and later wants to also sign in with Google, linking keeps their existing orders, settings, and RLS-scoped data intact under one identity, whereas treating the Google sign-in as a brand-new account would silently fragment their data across two separate user IDs with no data in common.

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What happens to the user ID when linking a new OAuth identity to an existing account? The user ID is randomized on every sign-in

✗ Try again, that's not it.

A brand-new user ID is always generated

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It stays the same - the new provider attaches to the existing user row

✓ Correct! Well done.

The old user ID is deleted

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What problem does identity linking prevent? Row Level Security being disabled

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Users being unable to sign in with email at all

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A user's data fragmenting across two separate accounts with no shared history

✓ Correct! Well done.

Realtime subscriptions failing

✗ Try again, that's not it.

More Related questions...

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