Greatest not null column

问题

I need to update a row with a formula based on the largest value of two DATETIME columns. I would normally do this:

GREATEST(date_one, date_two)

However, both columns are allowed to be NULL. I need the greatest date even when the other is NULL (of course, I expect NULL when both are NULL) and GREATEST() returns NULL when one of the columns is NULL.

This seems to work:

GREATEST(COALESCE(date_one, date_two), COALESCE(date_two, date_one))

But I wonder... am I missing a more straightforward method?

回答1:

COALESCE(GREATEST(date_one, date_two), date_one, date_two)

回答2:

My solution for multiple columns is:

SELECT NULLIF(
  GREATEST(
    NVL(NULL,     to_date('01011980','ddmmyyyy')), --COLUMN 1
    NVL(sysdate,  to_date('01011980','ddmmyyyy')), --COLUMN 2
    NVL(NULL,     to_date('01011980','ddmmyyyy')), --COLUMN 3
    NVL(sysdate-1,to_date('01011980','ddmmyyyy'))  --COLUMN 4
  ),to_date('01011980','ddmmyyyy')
) as greatest_date
FROM DUAL;

来源：https://stackoverflow.com/questions/2684090/greatest-not-null-column