데이터베이스 질문과 답변
WITH T AS(
SELECT NULL AS DT FROM DUAL UNION ALL
SELECT NULL AS DT FROM DUAL UNION ALL
SELECT '' AS DT FROM DUAL UNION ALL
SELECT '' AS DT FROM DUAL UNION ALL
SELECT '-' AS DT FROM DUAL UNION ALL
SELECT '-' AS DT FROM DUAL UNION ALL
SELECT 'A' AS DT FROM DUAL UNION ALL
SELECT 'B' AS DT FROM DUAL UNION ALL
SELECT 'C' AS DT FROM DUAL UNION ALL
SELECT 'D' AS DT FROM DUAL UNION ALL
SELECT 'E' AS DT FROM DUAL )
SELECT DT FROM T
WHERE NVL(DT,'-') = '-';
WITH T AS(
SELECT NULL AS DT FROM DUAL UNION ALL
SELECT NULL AS DT FROM DUAL UNION ALL
SELECT '' AS DT FROM DUAL UNION ALL
SELECT '' AS DT FROM DUAL UNION ALL
SELECT '-' AS DT FROM DUAL UNION ALL
SELECT '-' AS DT FROM DUAL UNION ALL
SELECT 'A' AS DT FROM DUAL UNION ALL
SELECT 'B' AS DT FROM DUAL UNION ALL
SELECT 'C' AS DT FROM DUAL UNION ALL
SELECT 'D' AS DT FROM DUAL UNION ALL
SELECT 'E' AS DT FROM DUAL )
SELECT DT FROM T
WHERE DT IN ( DT ,'')
위 두 쿼리의 결과과 다른데....왜 그런건지 이유좀 알수 있을까요?;;; ㅠㅠ
오라클에서 null은 equal(=) 로 비교할 수 없어서 질문자님이 원하시는 결과가 안나온거예요.
대부분의 컴퓨터 프로그래밍에서 NULL 과 '' 을 다르게 인식하는데.
오라클에서는 특이하게도 '' 을 NULL 로 인식합니다.
NULL 은 값이 아니므로 비교식에서 사용하면 결과는 항상 거짓(False)입니다.
) 버튼을 클릭하여 작성 하시면 됩니다.