What is an alternative to non-relational databases?

Relational databases.

Main differences:

Characteristic	Relational DBs	Non-relational DBs
Data structure	Tables with strict schema (SQL)	Diverse, flexible (documents, graphs, key-value)
Scalability	Vertical, more difficult horizontal scaling	Horizontal, easily scalable
ACID transactions	Supported	Depends on the DB type, often not or weaker
Schema flexibility	Low, requires migrations	High, schema can change
Performance	Good for structured queries	High for specific tasks (key-value, search)
Query complexity	SQL, powerful for complex joins	Diverse APIs, joins can be complex

Examples of relational DBs:

• MySQL
• PostgreSQL
• Oracle Database
• Microsoft SQL Server

The choice of an alternative depends on the specific project requirements: data type, need for scaling, schema flexibility, data integrity requirements, and query complexity.

-- Example of creating a table in a relational DB (SQL)
CREATE TABLE Users (
    UserID INT PRIMARY KEY,
    Name VARCHAR(255) NOT NULL,
    Email VARCHAR(255) UNIQUE
);

-- Example of inserting data
INSERT INTO Users (UserID, Name, Email) VALUES (1, 'Ivan Petrov', 'ivan.petrov@example.com');

// Example of data representation in NoSQL (document-oriented)
{
  "_id": 1,
  "name": "Ivan Petrov",
  "email": "ivan.petrov@example.com",
  "address": {
    "street": "Pushkina",
    "house": "1",
    "city": "Moscow"
  }
}