SQL (Structured Query Language) is a standard language used to manage and interact with relational databases. It allows users to store, retrieve, update, and delete data efficiently. SQL matters because nearly every modern application relies on structured data storage and access. Mastering SQL enables precise data handling, powering decision-making in businesses, apps, and analytics.

Relational databases store data in structured tables consisting of rows and columns, where each row is a record and each column is a field. These tables are linked using primary keys and foreign keys, creating relationships between different datasets. This model ensures data consistency, reduces redundancy, and supports complex queries. Relational databases are widely used in business, finance, and web applications for reliable data management.

Database models define how data is organized and accessed in a database system. The relational model uses tables and is ideal for systems like banking or inventory management. The document model (e.g., MongoDB) stores data as flexible JSON-like documents, perfect for content management systems. The key-value model (e.g., Redis) is used in caching and real-time data scenarios. The graph model handles relationships efficiently, making it suitable for social networks and recommendation engines.