안녕하세요.
SQL Manager 라는 클라이언트를 사용해보면서 궁금한 점이 생겨 문의해봅니다.
data = null 은 잘못된 비교라는 것을 압니다. data is null 로 비교를 해야 하지요.
그런데,
select 'a' = null as a, 'a' is null as b, 'a' is not null as c, null as d, '' as e;
이런 간단한 쿼리로 테스트를 해 보면,
![](data:image/gif;base64,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)
이런 결과가 나오게 됩니다.
보시다시피 a 는 null 도 아니고 boolean 도 아니고 빈문자열도 아닙니다.
이게 뭔가요?
쿼리짜는데 알 필요는 없지만 그냥 궁금합니다. ㅎㅎ
감사합니다. |