Entity integrity requires that each value of a primary key or unique constraint be unique within the table, and that there are no NULL values.
If a client application attempts to insert or update a primary key value, and provides values that are not unique, entity integrity is breached.
A breach in entity integrity prevents the new information from being added to the database, and instead sends the client application an error.
The application programmer should decide how to present this information to the user and enable the user to take appropriate action. The appropriate action in this case is usually just to provide a unique value for the primary key.
SAP Sybase IQ checks referential integrity for each UPDATE on a foreign key or candidate key, each DELETE on a candidate key, and each LOAD/INSERT on a foreign key. When a referential integrity violation occurs, UPDATE or DELETE requests are immediately denied and rolled back. LOAD/INSERT requests that violate referential integrity are also denied or rolled back. SAP Sybase IQ also optionally rejects rows that violate data integrity as specified by the user.