Column Defaults Encourage Data Integrity

Column defaults automatically assign a specified value to a particular column or set of columns whenever someone enters a new row into a database table.

The default value assigned requires no 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 who first modified a row in a table. Using column defaults encourages data integrity, but does not enforce it. Client applications can always override defaults.

• Supported Default Values
  Sybase IQ supports the following default values for columns:
• Default Value Restrictions
  Certain column default values are not supported.
• 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.
• Changing Column Defaults
  To change column defaults, use the same form of the ALTER TABLE statement you use to create defaults.
• Deleting Column Defaults
  To remove column defaults, modify them to be NULL.
• Supported Column Default Values
  You can load and insert column default values in Sybase IQ.
• Column Defaults in Sybase Central
  You can add, alter, and delete column defaults in Sybase Central using the Value tab of the column properties sheet.
• Date, Time, and Timestamp Defaults
  For columns with the DATE, TIME, or TIMESTAMP data type, you can use the CURRENT DATE, CURRENT TIME, TIMESTAMP, or CURRENT TIMESTAMP special value as a default. The default you choose must be compatible with the data type of the column.
• USER Defaults
  Assigning a DEFAULT USER to a column is an easy and reliable way of identifying the person making an entry in a database. This information may be required; for example, when salespeople are working on commission.
• The IDENTITY or AUTOINCREMENT Default
  The IDENTITY/AUTOINCREMENT default is useful for numeric data fields where the value of the number itself may have no meaning.
• The NEWID Default
  UUIDs (Universally Unique IDentifiers), also known as GUIDs (Globally Unique IDentifiers), can be used to uniquely identify rows in a table.
• The NULL Default
  For columns that allow NULL values, specifying a NULL default is exactly the same as not specifying a default at all.
• String and Number Defaults
  You can specify a specific string or number as a default value, as long as the column holds a string or number data type.
• Constant Expression Defaults
  You can use a constant expression as a default value, as long as the expression does not reference database objects.