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How To Use NULL as Conditions

Q

How To Use NULL as Conditions? - Oracle DBA FAQ - Understanding SQL Basics

✍: FYIcenter.com

A

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, 5278👍, 0💬

.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML