Can you explain what a unique identifier for a database record is, used for unambiguously recognizing each row?

A unique identifier for a record in a database is a field (or set of fields) that uniquely identifies each row in a table. Usually, this is a primary key. It guarantees that no record is duplicated and allows for quick finding, updating, or deleting of a specific record.

Commonly, the following are used for unique identifiers:

• Auto-incrementing integer values (e.g., SERIAL in PostgreSQL)
• UUID (Universally Unique Identifier) — 128-bit values that are practically impossible to duplicate

Example of creating a table with a unique identifier in PostgreSQL:

CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100)
);

Here, the id field is a unique identifier for each record.