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How To Use NULL as Conditions
How To Use NULL as Conditions? - Oracle DBA FAQ - Understanding SQL Basics
✍: FYIcenter.com
If 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
2007-04-23, 4917👍, 0💬
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