The Primary key is used to uniquely identify each row in a table. It can either be part of the actual record itself , or it can be an artificial field.
A primary key can consist of one or more fields on a table.
When multiple fields are used as a primary key, they are called a composite key.
Syntax:
column name datatype [CONSTRAINT constraint_name] PRIMARY KEY
Example:
CREATE TABLE Persons
(
Person_Id int NOT NULL PRIMARY KEY,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
);
