Constraints
When you create or alter a table, define constraints for the table. Constraints are used to check for appropriate data values whenever data is entered or updated in the table.
Constraints are checked at the end of every statement that modifies the table. If the constraint is violated, the DBMS returns an error and aborts the statement. If the statement is in a multi-statement transaction, the transaction is not aborted.
Note: For other mechanisms used to ensure the integrity of data in a table, including integrities and rules, see the Security Guide.
Define constraints using the CREATE TABLE or ALTER TABLE statements. In Director, use the New Table page. In VDBA, use the Create Table or Alter Table dialog.