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Oracle Database Interview Question:
How To Use NULL as Conditions in Oracle?
Submitted by: AdministratorIf you want to compare values against NULL as conditions, you should use the "IS NULL" or "IS NOT NULL" operator. Do not use "=" or "<>" against NULL. The sample script below shows you some good examples:
SELECT 'A' IS NULL FROM DUAL;
-- Error: Boolean is not data type.
-- Boolean can only be used as conditions
SELECT CASE WHEN 'A' IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
FALSE
SELECT CASE WHEN '' IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
TRUE
SELECT CASE WHEN 0 IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
FALSE
SELECT CASE WHEN NULL IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
TRUE
SELECT CASE WHEN 'A' = NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
-- Do not use "="
FALSE
SELECT CASE WHEN 'A' <> NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
-- Do not use "<>"
FALSE
SELECT CASE WHEN NULL = NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
-- Do not use "="
FALSE
Submitted by: Administrator
SELECT 'A' IS NULL FROM DUAL;
-- Error: Boolean is not data type.
-- Boolean can only be used as conditions
SELECT CASE WHEN 'A' IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
FALSE
SELECT CASE WHEN '' IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
TRUE
SELECT CASE WHEN 0 IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
FALSE
SELECT CASE WHEN NULL IS NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
TRUE
SELECT CASE WHEN 'A' = NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
-- Do not use "="
FALSE
SELECT CASE WHEN 'A' <> NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
-- Do not use "<>"
FALSE
SELECT CASE WHEN NULL = NULL THEN 'TRUE' ELSE 'FALSE' END
FROM DUAL;
-- Do not use "="
FALSE
Submitted by: Administrator
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