ASA SQL User's Guide
  Ensuring Data Integrity
    Using column defaults

Creating column defaults

You can use the CREATE TABLE statement to create column defaults at the time a table is created, or the ALTER TABLE statement to add column defaults at a later time.

Example 

The following statement adds a condition to an existing column named id in the sales_order table, so that it automatically increments (unless a client application specifies a value):

ALTER TABLE sales_order
MODIFY id DEFAULT AUTOINCREMENT

Each of the other default values is specified in a similar manner. For more information, see ALTER TABLE statement and CREATE TABLE statement.