For example, an employee should belong to only one department. However, constraints can allow permissions. For instance, the company can assign multiple cars to the same employee.

For example, you cannot use check constraints to reference other tables or to enforce uniqueness across multiple columns. In such cases, you may need to use other methods, such as triggers ...

According to the ANSI standards SQL:92, SQL:1999, and SQL:2003, a UNIQUE constraint should disallow duplicate non-NULL values, but allow multiple NULL values. SQL Server has always implemented a ...