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Lesson 3 — UNIQUE indexes
UNIQUE indexes enforce rules
An index is not only for speed. A UNIQUE index also guarantees that no two rows share the same value in that column. Trying to insert a duplicate raises sqlite3.IntegrityError, which your code can catch with try / except.
CREATE UNIQUE INDEX idx_cars_plate ON cars(plate)
Why it matters: "one account per email" must be guaranteed by the database itself — checking in app code alone fails when two sign-ups arrive at the same moment.
Want it another way?
Task
Write the CREATE UNIQUE INDEX on users(email). The duplicate sign-up should then be rejected.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
Test your knowledge
Test your knowledgeA quick 3-question quiz on this lesson — instant feedback.