Redundancy issues in databases

Redundancy means having multiple copies of the same data in the database. This problem occurs when the database is well normalized. Suppose the student details attribute table is: student ID, student name, university name, university ranking, course selection.

It can be seen that the values ​​of the attributes college name, university ranking, course are being duplicated, which may cause problems. Problems caused by redundancy include: insertion exceptions, deletion exceptions and update exceptions.

1. Insertion Exception

If the details of a student have to be inserted, whose course has not been decided yet, it cannot be inserted until the time course is decided for the student.

This problem occurs if the data record cannot be inserted without adding some other extraneous data to the record.

2. Deletion Exception

If you delete the student details in this table, then the university details will also be deleted, this should not be common knowledge.
This exception occurs when deleting a data record results in the loss of some irrelevant information that was stored as part of the record being deleted from the table.

3. Update exception
Assuming that the grade of the university changes, the change must be spread throughout the entire database, which will consume a lot of time and be computationally expensive.

If updates do not occur everywhere, the database will be in an inconsistent state.

Recommended tutorial: "mysql tutorial"//m.sbmmt.com/course/list/51.html

This article This article is a relevant introduction to redundancy issues in databases. I hope it will be helpful to friends in need!

The above is the detailed content of Redundancy issues in databases. For more information, please follow other related articles on the PHP Chinese website!