medium10 pts · first answer countssqlmissing-data

NOT IN returns no rows

This query returns zero rows even though many customers never ordered: SELECT * FROM customers WHERE id NOT IN (SELECT customer_id FROM orders). What is the most likely cause?

A.orders.customer_id contains a NULL, which makes every NOT IN check unknownB.NOT IN only works on text columnsC.The subquery returns too many rowsD.customers.id must be indexed for NOT IN to work

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