Constraints

You can enter constraint information in the form of default or initial values and validation rules in both the logical and physical model. You can define and attach validation rules, default values, or initial values to tables, columns, entities, and attributes.

• A default value is a specified value for a table, column, entity, or attribute if no value is explicitly supplied when a record is inserted into the table or an instance is inserted into an entity.
• A validation rule specifies a fixed list of valid values, minimum or maximum values or a range of values, or uses an expression to define some form of data validation code for a particular table, column, entity, or attribute.

Validation rules and default table and column values are generated with the appropriate data definition statements for your target DBMS, either actively through connection to the system catalog or to a DDL script.

Although constraint dialogs are provided, SQL constraint statements are not generated for the target servers that do not support constraints.

More information:

Add a Default or Initial Value for a Target Server

Default Value Editor

Attaching a System Generated Default or Initial Value to a Column