To define rules that help to provide data integrity
A constraint is used to define rules that help to provide data integrity. There are two different types of constraints, TABLE constraints, which do not require any column information and column constraints, which are specific to the column name specified. You must have ALTER privilege on the table. The table will be locked for EXCLUSIVE use during the operation.
|ONBEFOREDELETE / ONDELETE|
|ONBEFOREINSERT / ONINSERT|
|ONBEFOREUPDATE / ONUPDATE|