A relational database is a type of database that organizes data into structured tables (also called relations) consisting of rows and columns. Each table represents a specific entity, such as “customers” or “orders,” and columns define the attributes of that entity (e.g., “customer_id,” “name,” “email”). Rows contain individual records. Relationships between tables are established using keys: a primary key uniquely identifies a row in one table, and a foreign key in another table references that primary key to link related data. For example, an “orders” table might include a “customer_id” foreign key to associate each order with a customer in the “customers” table.
Developers interact with relational databases using SQL (Structured Query Language) to create, read, update, and delete data. SQL allows querying across tables using operations like JOINs, which combine data from multiple tables based on their relationships. For instance, a JOIN between “customers” and “orders” could retrieve a customer’s name alongside their order history. Relational databases enforce schema constraints, such as data types (e.g., integers, strings) and referential integrity (ensuring foreign keys point to valid primary keys), which helps maintain data accuracy. Popular relational database systems include MySQL, PostgreSQL, and Microsoft SQL Server.
Relational databases excel in scenarios requiring ACID (Atomicity, Consistency, Isolation, Durability) transactions, such as banking systems or e-commerce platforms. For example, transferring funds between accounts requires atomic updates to both accounts, which relational databases handle reliably. They also support normalization, a process of structuring data to minimize redundancy. While alternatives like NoSQL databases exist for unstructured data or scalability needs, relational databases remain a go-to choice for applications demanding structured, consistent, and interrelated data management. Their maturity, tooling, and widespread adoption make them a foundational tool for developers building transactional or reporting systems.