Primary Key

Primary Key:
A primary key is a field or combination of fields that uniquely identify a record in a table, so that an individual record can be located without confusion.
http://www.databasedev.co.uk/primary_foreign_key_constraints.html


A primary key is one which uniquely identifies a row of a table. this key does not allow null values and also does not allow duplicate values
http://www.allinterview.com/showanswers/15625.html


A primary key in a database, is simply a useful device (key) that makes each record unique.
Read more: http://wiki.answers.com/Q/What_is_the_purpose_of_a_primary_key_in_a_database#ixzz1sIudT06W