مجید اطلس باف

Special situations often arise in database development where it is convenient to temporarily disable constraints. For example, it is often easier to load initial values into a database one table at a time, without worrying with foreign key constraints and checks until all of the tables have finished loading. After the import is complete, you can turn constraint checking back on and know the database is once again protecting the integrity of the data. You can do this by using the following commands:

ALTER TABLE [TableName] NOCHECK CONSTRAINT [ConstraintName]
-- Do your updates here
ALTER TABLE [TableName] CHECK CONSTRAINT [ConstraintName]

In order to disable or enable all constraints use "ALL" instead of [ConstraintName] in the above commands.
Note that the only constraints you can disable are the FOREIGN KEY constraint, and the CHECK constraint. PRIMARY KEY, UNIQUE, and DEFAULT constraints are always active.

To read more about this subject visit the following page:

Microsoft SQL Server Constraints