If you do not code the referential constraints, then your DBMS will permit you to do improper things such as backing up related tables on different schedules. That means data integrity issues can arise if you have to recover using the backups without applying log records.

You enforce referential integrity by enabling it for a table relationship. Once enforced, Access rejects any operation that would violate referential integrity for that table relationship.

TO ENFORCE REFERENTIAL INTEGRITY:

1. IN THE DATABASE WINDOW, CLICK THE RELATIONSHIPS BUTTON ON THE TOOLBAR.
2. DOUBLE-CLICK THE JOIN LINE FOR THE RELATIONSHIP YOU WANT TO WORK WITH.
3. CHECK THE ENFORCE REFERENTIAL INTEGRITY BOX.

To enforce referential integrity rules, you can create a foreign key and references constraint, as the statement in Listing 1 shows. Also, you can establish the reference between SecondaryTable and PrimaryTable when you create SecondaryTable.

Referential integrity is violated when the relation to which a foreign key refers no longer exists. For example, if one deletes a donor from the Donor table, without also deleting the corresponding donations from the Donation table, then the DonorID field in the Donation record would refer to a non-existent donor.

For example, referential integrity ensures that every foreign key value in the DEPT column of the EMP table matches a primary key value in the DEPTNO column of the DEPT table. Two parent and dependent relationships exist between the DEPT and EMP tables.

Referential integrity is a database feature in relational database management systems. It ensures the relationships between tables in a database remain accurate by applying constraints to prevent users or applications from entering inaccurate data or pointing to data that doesn’t exist.

Cascading referential integrity constraints allow you to define the actions when a user tries to delete or update a key for which foreign keys exist. Cascading is used with the drop command when we want to drop a parent table even when a child table exists.

An example of a database that has not enforced referential integrity. In this example, there is a foreign key ( artist_id ) value in the album table that references a non-existent artist — in other words there is a foreign key value with no corresponding primary key value in the referenced table.

A referential integrity asserts a relationship between two tables such that the values in a column of one table must match the values in a column of the second table. There cannot be a child without a parent (that is, an orphan)—this constitutes a referential integrity violation.

When a referential integrity constraint is violated, the normal procedure is to reject the action. But a foreign key clause in SQL-92 can specify steps to be taken to change the tuples in the referenced relation to restore the constraint.

Enforcing Referential Integrity for a relationship in a Microsoft Access database can avoid the loss or inadvertent updating of data records.

Solution that is possible to correct such violation is if any insertion violates any of the constraints, then the default action is to reject such operation. Deletion operation: On deleting the tuples in the relation, it may cause only violation of Referential integrity constraints.

No, Foreign Key in a table doesn’t have to be unique in said table. BUT, as it is the Primary Key of another table, it must be unique in this table. No. No, foreign keys do not have to be unique.

Answer: No. We can’t have a Primary Key column with a NULL value. The reason for the same is very simple, primary key purpose is to uniquely identify records. This is the reason, Primary Key can’t have NULL values as they are not compared with any other value.

A table may have multiple foreign keys, and each foreign key can have a different parent table. Each foreign key is enforced independently by the database system. Therefore, cascading relationships between tables can be established using foreign keys.

A foreign key may not be null when it is part of a composite primary key in the child table.

FOREIGN KEY constraints are not enforced on temporary tables. FOREIGN KEY constraints cannot reference another column in the same table.

Foreign keys allow key values that are all NULL , even if there are no matching PRIMARY or UNIQUE keys. By default (without any NOT NULL or CHECK clauses), the FOREIGN KEY constraint enforces the match none rule for composite foreign keys in the ANSI/ISO standard.

Explanation: Each table is having only one primary key constraint and it contains only unique values.

A constraint is enforced only for the insert operation on a table. D. A constraint can be disabled even if the constraint column contains data.

The obvious problem with the lack of foreign keys is that a database can’t enforce referential integrity and if it wasn’t taken care of properly at the higher level then this might lead to inconsistent data (child rows without corresponding parent rows).