Databases

A database is an organized collection of data stored electronically so it can be easily accessed, managed and updated. All modern applications — banking, shopping, social media — depend on databases.

• Relational Databases (SQL): Store data in tables with rows and columns
• NoSQL Databases: Store data as documents, key-value pairs or graphs

• Table – collection of records
• Row – single record
• Column – attribute of data
• Primary Key – unique identifier
• Foreign Key – link between tables

• SELECT – retrieve data
• INSERT – add data
• UPDATE – modify data
• DELETE – remove data

NoSQL databases store flexible and unstructured data. They are commonly used in modern web and cloud applications. Example: MongoDB stores data in JSON-like documents.

Databases ensure reliable operations using ACID:

• Atomicity – all or nothing
• Consistency – valid data
• Isolation – operations don’t interfere
• Durability – data remains saved

• User login systems
• Online payments
• E-commerce orders
• Application data storage