• The primary key constraint uniquely identifies each record in a database table
• Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table
• Primary keys must contain unique values
• A primary key column cannot contain NULL values

CREATE TABLE Employee
(
    empid int NOT NULL PRIMARY KEY,
    empname varchar(255) NOT NULL,
    age varchar(255),
    address varchar(255),
    city varchar(255)
)