Constraints

Constraints are business logic that your database server enforces for you. They limit the possible values that users can enter into specified columns, enforcing referential integrity. When you create constraints in the Database Designer, they conform to the ANSI standard for creating and altering tables.

The Database Designer accepts five types of constraints:

• Check Constraints
  
• Default Constraints
  
  
• Unique Constraints
  
  
• Primary Key Constraints
  
  
• Foreign Key Constraints