A Primary Key is a special relational database table column key or combination of columns designed to uniquely identify all table records. A Primary Key must contain a unique value for each row of data. It cannot contain null values. A Primary Key is either an existing table column or a column that is specifically generated by the database according to a defined sequence. The best option is to create a separate primary key in a new column named CUSTOMER_ID. The database automatically generates a unique number each time a customer is added with unique identification. As this key is created, the column is designated as the primary key within the SQL script that creates the table, and all null values are automatically rejected.