Why is data uniqueness constraint used in databases?

The uniqueness constraint in a database is used to ensure that the values in a specific column or set of columns are unique across all rows in the table. This helps to:

• Prevent data duplication, for example, so that two users do not have the same email.
• Ensure data integrity and correctness of business logic.
• Simplify search and record identification.

Example in SQL:

CREATE TABLE users (
  id INT PRIMARY KEY,
  email VARCHAR(255) UNIQUE
);

Here, the email column cannot contain duplicate values.