Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 6: Constraints
Dropping Rules
If you want to completely eliminate a rule from your database, you use the same DROP syntax that we’ve
already become familiar with for tables:
Defaults
DROP RULE
Defaults are even more similar to their cousin — a default constraint — than a rule is to a CHECK constraint.
Indeed, they work identically, with the only real differences being in the way that they are
attached to a table and the default’s (the object, not the constraint) support for a user-defined data type.
The syntax for defining a default works much as it did for a rule:
CREATE DEFAULT
AS
Therefore, to define a default of zero for our Salary:
CREATE DEFAULT SalaryDefault
AS 0;
Again, a default is worthless without being bound to something. To bind it, we make use of sp_bindefault,
which is, other than the procedure name, identical in syntax to the sp_bindrule procedure:
EXEC sp_bindefault ‘SalaryDefault’, ‘Employees.Salary’;
To unbind the default from the table, we use sp_unbindefault:
EXEC sp_unbindefault ‘Employees.Salary’;
Keep in mind that the futureonly_flag also applies to this stored procedure; it is just not used here.
Dropping Defaults
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The concept of defaults vs. DEFAULT constraints is wildly difficult for a lot of people
to grasp. After all, they have almost the same name. If we refer to “default,” then we
are referring to either the object-based default (what we’re talking about in this section),
or a shorthand to the actual default value (that will be supplied if we don’t
provide an explicit value). If we refer to a “DEFAULT constraint,” then we are talking
about the non-object-based solution — the solution that is an integral part of the
table definition.
If you want to completely eliminate a default from your database, you use the same DROP syntax that
we’ve already become familiar with for tables and rules:
DROP DEFAULT