How To Use NULL as Conditions?

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
How To Concatenate Two Text Values?
There are two ways to concatenate two text values together:
CONCAT() function.
'||' operation.
Here is some examples on how to use them:
SELECT 'FYI' || 'Center' || '.com' FROM DUAL;
FYICenter.com
SELECT CONCAT('FYICenter','.com') FROM DUAL;
FYICenter.com