Please tell about relational databases in general. They include Postgres, I will specify its specifics.

Relational databases (RDBs) are database management systems that store data in the form of tables consisting of rows and columns. Main characteristics:

• Data is organized into tables with a clearly defined schema (structure).
• Tables are linked through relationships (foreign keys).
• They use SQL language for queries, updates, and data management.
• They ensure data integrity through constraints, transactions, and locking mechanisms.

PostgreSQL is one of the most popular open-source relational DBMSs. Features of Postgres:

• Support for advanced data types (JSON, XML, arrays, etc.).
• Powerful indexing system to speed up queries.
• Support for transactions with isolation levels.
• Extensibility: you can add your own functions, types, operators.
• Active community and stability.

In the context of Node.js, libraries like pg are often used to work with Postgres, allowing execution of SQL queries and connection management.

Example of a simple query in Node.js using pg:

const { Client } = require('pg');
const client = new Client({ connectionString: process.env.DATABASE_URL });

async function getUsers() {
  await client.connect();
  const res = await client.query('SELECT * FROM users');
  console.log(res.rows);
  await client.end();
}

getUsers();

Thus, relational databases provide structured data storage and efficient data access, and Postgres is a powerful tool with rich functionality for solving a wide range of tasks.