Defaults

In SQL Server, each column in a record must contain some value ¾ even if that value is NULL. You determine whether a column can accept null values by the datatype, default, or constraint you specify.

Defaults specify the value that SQL Server will insert when a user does not enter a value (in either a NULL or NOT NULL column). For example, in a table with a column called price, if the user does not know the price of an item, you can instruct SQL Server to enter "???" or "fill in later."

The easiest way to specify defaults is to define DEFAULT constraints when you create a table.

You can also create defaults and then bind them to columns or to user-defined datatypes so that whenever no entry is entered into that column or whenever a column is assigned that user-defined datatype, the default automatically takes effect. For details on creating defaults, see the CREATE DEFAULT statement in the Microsoft SQL Server Transact-SQL Reference.