62. Churned Customers (EXCEPT)
MediumSet OperationsEXCEPTanti-joindeduplication
EXCEPT returns rows in the first set that are not in the second ("in A but not B"). It dedupes and compares whole rows, making it a clean way to express set difference.
Task: a customer has churned if they bought last year but not this year. Return the churned customers.
Return a single column customer. Order by customer ascending.
Tables
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Expected outputrows must come back in this order
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