Null Clause
The WITH|NOT NULL clause in the column specification specifies whether a column accepts null values.
This clause has the following format:
WITH NULL | NOT NULL
WITH NULL
Indicates that the column accepts nulls. If no value is supplied by the user, null is inserted as the default value.
NOT NULL
Indicates that the column does not accept nulls. If the DEFAULT clause is omitted or NOT DEFAULT is specified, the column is mandatory.