How set 0 with MAX function when it is NULL?

问题:

I would like to understand how to set 0 value of the attribute when it is NULL with MAX function. For example:

Name columns:
number - date

Values:
10 - 2012-04-04
11 - 2012-04-04
12 - 2012-04-04
13 - 2012-04-15
14 - 2012-06-21
 1 - 2013-07-04

Number is incremental field, but it has set itself 1 when new year has come. But result of:

SELECT (MAX(number)+1) number WHERE date LIKE "2014%" 

is NULL and not 1 because MAX(number) is NULL and not 0

回答1:

Well, as there is no date like 2014, you would expect null, because the maximum of nothing is actually not anyting.

But do this:

COALESCE(MAX(number),0)

Which means: get the first non-null thing from the next list, so if your max is null, it'll give you 0

回答2:

COALESCE works, but IFNULL seems clearer to me.

IFNULL(MAX(number), 0)

If the first expression is not NULL, IFNULL() returns the expression itself, otherwise it returns the second parameter. IFNULL() returns a numeric or string value, depending on the context in which it is used.