Handling Null in Greatest function in Oracle

Question

I want to compare two dates from two columns and get the greatest and then compare against a date value.The two column can hold NULL values too.For example I want the below OUTP

Answer 1

use NVL to solve this however complicity will be increased based of number of compared columns :

select A.*, *greatest("COL A", "COL B") "DIRECT COMPARE"*, **greatest(nvl("COL A", "COL B"), nvl("COL B", "COL A")) "NVL COMPARE"**
from (
SELECT NULL "COL A", SYSDATE "COL B", SYSDATE "NEEDED RESULT" FROM DUAL UNION
SELECT SYSDATE - 180 , NULL  , SYSDATE - 180 FROM DUAL UNION
SELECT SYSDATE - 180 , SYSDATE , SYSDATE FROM DUAL ) A;