A null represents an undefined or unknown value and is specified by the keyword null. A null is not the same as a zero, a blank, or an empty string. You can assign a null to any nullable column when no other value is specifically assigned. For more information about defining nullable columns, see CREATE--Create a Table.

The ifnull function and the is null predicate enable you to handle nulls in queries. For details, see Ifnull and Is Null Comparison.