SQL Database

SQL Database: An Introduction

What is an SQL Database?

An SQL database is a structured collection of data organized into tables. SQL (Structured Query Language) is used to interact with the database for storing, retrieving, updating, and managing the data efficiently. SQL databases are relational, meaning data is stored in a tabular format with relationships between tables.

Key Features of an SQL Database

1. Relational Structure: Data is stored in tables consisting of rows and columns.
2. Standardized Language: SQL is a universal language supported by most database systems.
3. Data Integrity: Enforces constraints like primary keys, foreign keys, and unique keys.
4. ACID Compliance: Ensures atomicity, consistency, isolation, and durability for transactions.
5. Scalability: Supports large datasets and complex queries.

Components of an SQL Database

1. Tables: The primary structure where data is stored.
2. Columns: Define the attributes or fields of the table.
3. Rows: Represent individual records in a table.
4. Constraints: Rules like PRIMARY KEY, FOREIGN KEY, and UNIQUE to maintain data integrity.
5. Indexes: Improve the speed of data retrieval.
6. Views: Virtual tables created from SQL queries.

Popular SQL Database Management Systems

1. MySQL: Open-source, widely used for web applications.
2. PostgreSQL: Advanced features like JSON support and full ACID compliance.
3. SQL Server: Microsoft's RDBMS with robust integration for Windows platforms.
4. SQLite: Lightweight, file-based database suitable for small-scale applications.
5. Oracle Database: Enterprise-level database with advanced performance and scalability.

SQL Database Operations

1. Creating a Database

CREATE DATABASE my_database;

2. Selecting a Database

USE my_database;

3. Creating a Table

CREATE TABLE employees (
    employee_id INT PRIMARY KEY,
    employee_name VARCHAR(100),
    department VARCHAR(50),
    salary DECIMAL(10,2)
);

4. Inserting Data

INSERT INTO employees (employee_id, employee_name, department, salary)
VALUES (1, 'John Doe', 'IT', 75000);

5. Querying Data

SELECT * FROM employees;

6. Updating Data

UPDATE employees
SET salary = 80000
WHERE employee_id = 1;

7. Deleting Data

DELETE FROM employees
WHERE employee_id = 1;

Relational Concepts in an SQL Database

1. Primary Key: Uniquely identifies each row in a table.
2. Foreign Key: Establishes a relationship between two tables.
3. Normalization: Organizes data to reduce redundancy and improve integrity.
4. Joins: Combines rows from two or more tables based on a related column.

Example of a Relational Database

Table: Employees

Table: Departments

Join Example

SELECT e.Employee_Name, d.Department_Name
FROM Employees e
INNER JOIN Departments d
ON e.Department = d.Department_Name;

SQL Database Use Cases

1. Web Applications: Manage user data, product catalogs, and transactions.
2. Enterprise Applications: HR systems, CRM, and inventory management.
3. Data Analytics: Store and query large datasets for reporting.
4. Mobile Apps: Lightweight databases like SQLite for offline storage.