ASA SQL User's Guide
  Ensuring Data Integrity

Using column defaults

Column defaults automatically assign a specified value to particular columns whenever someone enters a new row into a database table. The default value assigned requires no any action on the part of the client application, however if the client application does specify a value for the column, the new value overrides the column default value.

Column defaults can quickly and automatically fill columns with information, such as the date or time a row is inserted, or the user ID of the person typing the information. Using column defaults encourages data integrity, but does not enforce it. Client applications can always override defaults.

Supported default values 

SQL supports the following default values:

• A string specified in the CREATE TABLE statement or ALTER TABLE statement

• A number specified in the CREATE TABLE statement or ALTER TABLE statement

• An automatically incremented number: one more than the previous highest value in the column

• Universally Unique Identifiers (UUIDs) and Globally Unique Identifiers (GUIDs) generated using the NEWID function.

• The current date, time, or timestamp

• The current user ID of the database user

• A NULL value

• A constant expression, as long as it does not reference database objects

Creating column defaults
Modifying and deleting column defaults
Working with column defaults in Sybase Central
Current date and time defaults
The user ID default
The AUTOINCREMENT default
The NEWID default
The NULL default
String and number defaults
Constant expression defaults