Snippet

Defining Unique Identifiers with Primary Keys

A PRIMARY KEY constraint uniquely identifies each record in a database table. Primary keys must contain unique values and cannot contain NULL values.

snippet.sql

sql

CREATE TABLE users (
    user_id INT NOT NULL,
    username VARCHAR(50) NOT NULL,
    CONSTRAINT pk_users PRIMARY KEY (user_id)
);

Breakdown

CREATE TABLE users (

Starts the creation of a new table named users.

user_id INT NOT NULL,

Defines an integer column that cannot store NULL values.

username VARCHAR(50) NOT NULL,

Defines a variable-length character column up to 50 characters.

CONSTRAINT pk_users PRIMARY KEY (user_id)

Enforces unique values and non-nullability for user_id as the primary key.

);

Closes the table creation statement.