Questions

A primary key is a special relational database table column or combination of columns designated to uniquely identify all table records. That is, A primary key is a column or set of columns in a table that uniquely identifies tuples (rows) in that table.

A primary key, also called a Primary Keyword.

Main Features Primary key are ::

It must contain a unique value for each row of data.

It cannot contain null values.

The system unit of a personal computer typically contains microprocessor, disk controller and serial interface but it does not contain modem.

In 454 B.C, laws were codified in Rome. The laws were written on tablets of wood and were known as 'Laws of Twelve Tables'.

In Spain, where there were no protestants, a soldier named lgnatius Loyola started an organisation for clergymen to work wholly as 'soldiers of jensus' in the service of the Church. Its members came to be called jesuits. They went from place to place and won back followers in France and Germany. They established missions in india, china, Africa and the Americas to gain new adherents. The Jesuit Schools which they started to strengthen the Roman Catholic  Church are still in existence in many countries of the world.

The greatest single drop of the waterfall, Salto Angel of Venezuela, measures 807m and the width at the base is about 150 m. From top to bottom the Angel falls measures 979 m - almost 1 km.

Prices do not reflect the full social cost of production is an example of Market failure.

A market failure occurs when the supply of a good or service is insufficient to meet demand. This results in an inefficient distribution of resources among market participants.

It also occurs if externalities are not accounted for.

If a firm fails to maximize its profits this is not a general market failure.