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 Oracle CASE... WHEN structure in your select:

SELECT COLA, COLB, CASE
  WHEN (COLA >= COLB OR COLB IS NULL)
    THEN COLA
  ELSE COLB
  END
  AS OUTPUT
FROM ...