Relational Database Management System (RDBMS)
Master relational database foundations and MySQL: from relational models, tuples, attributes, degree, and cardinality to Primary vs Candidate keys, DDL (CREATE, ALTER, DROP), DML (INSERT, SELECT, UPDATE, DELETE), and advanced SQL clauses.
Why RDBMS? Limitations of File Systems
Prior to DBMS, organizations relied on file processing systems where data was maintained in flat files. This led to serious operational bottlenecks that modern relational databases resolve.
1. Data Redundancy
Same data is duplicated across multiple disparate files (e.g., student address stored separately in library and fee files), wasting disk storage and leading to inconsistency.
2. Data Inconsistency
When redundant data is updated in one file but forgotten in another, conflicting copies coexist, destroying the reliability of organizational information.
3. Integrity & Security Issues
Difficult to enforce business constraints (e.g., age > 18, salary > 0) across raw text files, and lack of fine-grained multi-level user access control.
Essential Relational Terminology
A two-dimensional grid of rows and columns storing data about a specific entity (e.g., Student).
A horizontal row in a relation representing a single complete data entity instance.
A vertical column representing a specific characteristic or property of the entity.
The pool of permissible, valid atomic values from which an attribute can derive values.
The total number of attributes (columns) present in a relation.
The total number of tuples (rows) present in a relation.
Classification of Relational Keys
Any minimal attribute (or set of attributes) that can uniquely identify each tuple in a relation without redundancy.
The chosen candidate key designated by the database administrator to uniquely identify tuples. Cannot contain NULL or duplicate values.
All candidate keys that were not chosen as the Primary Key. (Alternate Keys = Candidate Keys - Primary Key).
A non-key attribute in one relation whose values match the Primary Key of another relation, establishing a parent-child link (Referential Integrity).