Relational Database Management System

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 A Relational Database is any database structured based on the relational data model. A Relational Database Management System (RDBMS) is the software used to manage these databases.

RDBMS is the foundation of SQL and serves as the backbone for modern database systems like MySQL, Oracle, and Microsoft Access.

Key concepts in RDBMS include Databases, Tables, Tuples (Rows), Attributes (Columns), Schemas, and Keys, which are essential for organizing and managing data efficiently. These concepts are commonly referred to as RDBMS Jargons and are fundamental to understanding relational databases.


RDBMS Jargons:

Relational Databases

One of the most popular Relational Databases is MySQL, an open-source SQL database that runs on multiple platforms, including Windows, Linux, and macOS. Other widely used relational databases include Oracle, Microsoft SQL Server, and MS Access.

Key Features of RDBMS

  • High Availability – Ensures continuous access to data
  • High Performance – Optimized for speed and efficiency
  • Robust Transactions – Supports reliable and secure data operations
  • Easy Management – Simplifies database administration
  • Cost-Effective – Lower costs compared to some proprietary solutions

Table in a Relational Database

In a relational database, a table is a structured collection of data organized into rows and columns. It provides a simple and intuitive way to represent relationships between data.

While a true relation in database theory does not allow duplicate rows, a table in an RDBMS can contain duplicates unless constraints like primary keys are applied to enforce uniqueness.



Column in a Relational Database

A table in a relational database consists of multiple rows and columns. Each column represents a specific type of data and is also referred to as an attribute.

For example, in an Employee table, common attributes might include ID, Name, Age, and Salary. Each attribute is designed to store values of a specific data type, known as the Attribute Domain. For instance, the Name column would store only text, not numbers.

In database terminology, a column or attribute is a vertical entity within a table that ensures data is stored in a structured and organized manner.



Primary Key and Alternate Key

A Primary Key is a candidate key selected to uniquely identify each row (record) in a table. Every row must have a unique and non-null value for its primary key.

If a table has multiple candidate keys, the ones not chosen as the primary key are called Alternate Keys.

When a primary key consists of multiple attributes (columns) instead of just one, it is known as a Composite Primary Key. This is used when a single column is not sufficient to uniquely identify records.

Foreign Key in a Relational Database

A Foreign Key is a column (or set of columns) in one table that acts as a reference to the Primary Key of another table. It establishes a relationship between the two tables, ensuring referential integrity.

  • A foreign key must match the entire primary key of the referenced table. If the primary key is composite (consists of multiple attributes), the foreign key must also be composite.
  • Unlike primary keys, foreign key values do not have to be unique and can contain null values.
  • In a composite foreign key, either all attributes must be null, or none can be null—partial null values are not allowed.

Super Key and Candidate Key

A Super Key is an attribute or a set of attributes that uniquely identifies each row (tuple) in a table.

From the set of super keys, the minimal keys (i.e., those without unnecessary attributes) are selected as Candidate Keys. A Candidate Key is a super key that contains no redundant attributes.

Since a Primary Key is chosen from the candidate keys, every primary key is a candidate key, but not every candidate key is a primary key.

In short:

  • Super Key → Can have extra attributes.
  • Candidate Key → A minimal super key (no extra attributes).
  • Primary Key → A chosen candidate key for uniquely identifying rows.

Composite Key (Compound Key)

A Composite Key (also called a Compound Key) is a key that consists of two or more attributes to uniquely identify rows in a table. It is used when a single attribute is not enough to ensure uniqueness.

For example, in a Student_Course table that tracks which students are enrolled in which courses, neither Student_ID nor Course_ID alone may be unique, but together (Student_ID, Course_ID) form a composite key to uniquely identify each record.









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