Redundancy Issues in a Database in DBMS

Here, we are going to learn about the redundancy issues in a Database in Database management system (DBMS).
Submitted by Anushree Goswami, on July 11, 2019

Redundancy takes place when there are more than one or multiple copies of the same relation in a database. Simply the storage of same or similar value more than once in the field is referred to as Redundancy.

For e.g. – Let's consider this Employee Table.

EmpID EmpName Age Salary Department

The similarity among the field values of the age and salary comes under the Redundancy in the database. Redundancy can lead to three types of issues:

  1. Insertion Anomaly
  2. Updation Anomaly
  3. Deletion Anomaly

1) Insertion Anomaly

Insertion Anomaly occurs when a particular detail is needed to be inserted in a relationship but the detail has some missing data, due to which it is not able to be inserted inside the database.

For e.g. – In the table of employee, suppose we want to enter this data.

EmpID EmpName Age Salary Department
4 Suresh 33 45000

Now, unless the department is specified for this particular employee, it is not possible to alter the database with this data.

Insertion Anomaly mostly occurs when some additional data is missing from the detail.

2) Updation Anomaly

In Updation Anomaly, the updation of particular redundant field value consumes a lot of time and it is costly too.

For e.g. – Let us consider in the table of employee, we want to update the salary of all the employees from 40000 to 42000. That will take time.

Since mostly the database is large, it takes a lot of time in order to update any data if they are redundant. It is costly as well, as the many databases need to get updated together. If anyone of the database left out, then it results in the inconsistency of the data.

3) Deletion Anomaly

In Deletion Anomaly, some unrelated data also get deleted with the preferred one. This result in the loss of data which we don't want to lose.

For e.g. – Let us consider in the table of an employee, we want to delete the employee record, and then with that, we will also lose the department details as well.

Deletion of some unwanted data results into the deletion of the data stored as a record in the database as some additional important information. This happens in Deletion Anomaly.

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