Question

List and describe update anomalies.

Answer 1

In DBMS, when the same data is stored multiple times unnecessarily in a database, it is known as redundancy of data, which creates problems like the inconsistency of the data and makes the data storage inefficient as we are storing repeated data number of times which make the database table size very large. Due to this inconsistency, 3 types of update anomalies can arise.

1. Insertion Anomalies - When certain data cannot be inserted into the database without the presence of other data. For example - If we have a student table in a database in which we have attributes like student_id, student_name, branch_name, branch_HOD. So in each tuple, we have to enter branch_name and Branch_HOD, which causes redundancy in the database. So, if we want to insert a new student of CSE branch whose branch data is not stored previously, then we cannot add the student details into it
2. Deletion Anomalies - If we want to delete some unwanted data, then it causes the deletion of important data. For example, if I want to delete the existing student details of a particular branch (CSE), then the details of the branch-like branch_name and branch_HOD will also get deleted.
3. Modification Anomalies - If we want to modify a single piece of the data in the database, then we need to update it all places in the database. For example, if the HOD of CSE branch has changed, then we need to update it in each row of CSE student rows.