When you add a new column to a table, the column is initialized with its default value for all existing rows. If NOT NULL is specified, a default value must also be specified.
You can add a column to a table using the ADD COLUMN clause of the SQL ALTER TABLE statement.
The altered table may consist of up to 8000 columns. The sum of the byte counts of the columns must not be greater than 32766 or, if a VARCHAR or VARGRAPHIC column is specified, 32740. If a LOB column is specified, the sum of record data byte counts of the columns must not be greater than 15 728 640.