Thread: Primary key in SQL

I am learning SQL database language. I have little bit knowledge of SQL. But I am quit confused about ‘primary key’. I want to know what the need of using primary key is. Any suggestion would be highly appreciated.

The primary key can represent one or more fields in a table. When the primary key represents some fields, it is called composite key. It is possible to give the primary key while creating the table (using CREATE TABLE) or replacing the structure of the existing table (through ALTER TABLE).