What is the difference between relational databases and NoSQL?

Relational databases (RDBMS) are based on tables with a clearly defined schema (the schema fixes the structure of data and column types). They use SQL for queries and support transactions with ACID properties, ensuring data integrity.

NoSQL databases are more flexible, do not require a fixed schema, and can store data in various formats: documents, key-value, graphs, column stores. They often scale horizontally and are optimized for large volumes of data and high write speeds, but may not guarantee strict consistency.

Examples of differences:

• RDBMS: PostgreSQL, MySQL
• NoSQL: MongoDB (documents), Redis (key-value), Cassandra (column)

The choice depends on requirements for data structure, scalability, and consistency.