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

You might try the following:

SELECT cola, colb, COALESCE( GREATEST( cola, colb ), cola, colb ) AS output
  FROM yourtable;

The reason for COALESCE() is that GREATEST() returns NULL if either of the parameters is NULL.