BeginnerCoder
DonateLesson 16 — EXISTS
EXISTS: is there at least one?
EXISTS (subquery) is true when the subquery returns at least one row. It is usually correlated: for each customer, check whether an order exists for them. The database can stop at the first match, so it is fast. NOT EXISTS finds rows with no match.
SELECT title FROM courses c
WHERE EXISTS (SELECT 1 FROM signups s WHERE s.course_id = c.id)
Why it matters: "customers who ordered", "users who never logged in" — yes/no questions about related rows.
Fill in the WHERE inside EXISTS so it matches orders of the current customer. Expected: Ann and Cy.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
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