MSDN Documentation

Database Basics

This section provides a foundational understanding of databases, their core concepts, and how they are used in modern software development. Whether you're a beginner or looking to refresh your knowledge, this guide covers the essential building blocks.

What is a Database?

A database is an organized collection of structured information, or data, typically stored electronically in a computer system. Databases are designed to efficiently store, retrieve, and manage data. They are the backbone of almost all applications, from simple websites to complex enterprise systems.

Types of Databases

Databases can be broadly categorized into several types based on their structure and the way they store data:

• Relational Databases (SQL): These databases organize data into tables with rows and columns. Relationships between tables are defined using keys. Popular examples include MySQL, PostgreSQL, SQL Server, and Oracle.
• NoSQL Databases: This category encompasses a variety of database types that do not follow the traditional relational model. They are often used for large-scale data processing, real-time web applications, and handling unstructured or semi-structured data. Examples include MongoDB (document-based), Redis (key-value), Cassandra (column-family), and Neo4j (graph).
• NewSQL Databases: These databases aim to provide the scalability of NoSQL with the ACID guarantees of relational databases.

Key Database Concepts

• Tables: In relational databases, data is stored in tables. Each table represents a type of entity (e.g., "Customers", "Products").
• Rows (Records): Each row in a table represents a single instance of the entity (e.g., a specific customer, a particular product).
• Columns (Fields/Attributes): Each column represents a specific piece of information about the entity (e.g., "CustomerID", "FirstName", "Price").
• Primary Key: A column or a set of columns that uniquely identifies each row in a table.
• Foreign Key: A column in one table that refers to the primary key in another table, establishing a link or relationship between them.
• Schema: The blueprint of a database, defining its structure, tables, columns, data types, and relationships.
• SQL (Structured Query Language): The standard language used to communicate with and manage relational databases. It's used for querying, inserting, updating, and deleting data.

Common SQL Operations

SQL commands are used to interact with relational databases. Here are some fundamental operations:

• SELECT: Used to query data from one or more tables.

  SELECT column1, column2 FROM table_name WHERE condition;

• INSERT: Used to add new records into a table.

  INSERT INTO table_name (column1, column2) VALUES (value1, value2);

• UPDATE: Used to modify existing records in a table.

  UPDATE table_name SET column1 = new_value WHERE condition;

• DELETE: Used to remove records from a table.

  DELETE FROM table_name WHERE condition;

Database Management Systems (DBMS)

A Database Management System (DBMS) is software that enables users to create, maintain, and control access to a database. It acts as an interface between the user or application and the database itself. Examples include MySQL, PostgreSQL, Microsoft SQL Server, Oracle Database, and MongoDB.

Data Integrity and Normalization

Data Integrity refers to the accuracy, consistency, and reliability of data throughout its lifecycle. Techniques like constraints (e.g., primary keys, foreign keys, unique constraints) and data type enforcement help maintain integrity.

Normalization is a database design technique used to reduce data redundancy and improve data integrity by organizing columns and tables in a way that ensures dependencies are properly enforced by database integrity constraints. It typically involves dividing larger tables into smaller, less redundant tables.