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Answer with explaination

In relational database,to identify uniquely each row in a table we must use primary key. 
 
A relational database consists a collection of tables which stores data about users.Relational database management system is the way to retrieve data from recored data or information in form of tables.
 
Each table must have a unique indentifier named as primary key which provides uniqueness to the table.Sometimes,we have number of tables and it becomes so difficult to determine or query on table which can give data from the database.So in that case primary key plays a significance role in querying a table.Often, primary key is made up from one column only to identify the uniqueness of record or row.
 
On the other hand compound key  used multiple columns to identify record uniquely.
 

Example

Emp_ID           Firstname         Lastname            Phone

1005              Ram               Singh                6766654355

1069             Sonu               Chand               7888887821





Here primary key is the Emp_ID.

 

100 points
5