How to max() make null as biggest value?

Hi , guys ,
I am newbie for sql, I have a problem when using max() function, I  
need get null when there are null in the value list, or return the  
largest value as usual, who can do this?

i.e.  max([1,2,3,4,5]) => 5
max([1,2,3,4,5,null]) => null

thanks in advance!

Feixiong
feixiongli@gmail.com