https://leetcode.com/problems/find-customer-referee/
MySQL uses three-valued logic "TRUE", "FALSE" and "UNKNOWN".
Anything compared to NULL evaluates to the third value: UNKNOWN.
]That’s why MySQL provides the IS NULL and IS NOT NULL operators to specifically check for NULL.
select name
from Customer
where referee_id is null or referee_id != 2'Coding Interview' 카테고리의 다른 글
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