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

Something like

SELECT CASE WHEN ColA is NULL and ColB is NULL then NULL
WHEN coalesce(ColA, '01/01/1753')>coalesce(ColB, '01/01/1753') then ColA
ELSE ColB END as Output