We use IFNULL operator in MySQL to get a non-null value for a column with null value.
If expr1 is not null then expr1 is returned. If expr1 is null then expr2 is returned.
Eg. SELECT name, IFNULL(id,’Unknown’) AS ‘id’ FROM user;
If id is not null then id is returned. If id is null then Unknown is returned.Read the full book at www.amazon.com