Find Customer Referee

Find the names of the customer that are not referred by the customer with id = 2.
Return the result table in any order.
문제링크

조건정리
ID가 2인 고객에게 referred 되지 않은 고객 찾기

풀이

SELECT name
FROM customer
WHERE referee_id <> 2  
      OR referee_id iS NULL

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