Quote Originally Posted by Jasdoif View Post
If the SQL standard didn't specify that NULLs are to be excluded before determining the maximum, that is indeed what should happen. (If there's nothing but NULLs, the result is then NULL.)
But, it's the rules set out in the SQL standard that define the meaning of "NULL" in SQL. And in this instance at least, they are clearly not treating it as "unknown", but more like "no value".