Primary Keys and Auto Increment Fields in MySQL

Answer

Primary Key:
A primary key is used to uniquely identify a row in a table. A table can have only one primary key. The values in a single column to store primary key are unique. More one column can be used as a primary key. When used, the combination of column values must be unique.

Auto Increment attribute:
The Auto Increment attribute is used to generate unique values for new rows. Value once used by a row, can not be used for another row.

The following example illustrates the use of both primary key and auto increment attribute.

CREATE TABLE Products (
id NOT NULL AUTO_INCREMENT,
product_name CHAR(30) NOT NULL,
PRIMARY KEY (id)
);