When and why is it recommended to specify a primary key in a database?

It is recommended to always specify a primary key in a database whenever it is necessary to uniquely identify each record in a table. This ensures data integrity and allows for efficient search, update, and delete operations.

Main reasons for specifying a primary key:

• Uniqueness: guarantees that there will be no duplicates in the table based on the key field.
• Indexing: the primary key is automatically indexed, which speeds up queries.
• Relationships: used to establish relationships between tables (foreign keys).

For example, in a users table, the id field is often made the primary key:

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