Define an extension table and its purpose.

An extension table, in the context of databases, is a secondary table that is linked to a primary table. It contains additional attributes that are not defined in the original or primary table. The purpose of using an extension table is to avoid data redundancy and to maintain database normalization. By segregating less frequently used or optional attributes into an extension table, we can efficiently organize and store data. For example, consider a primary table 'Employees' that stores basic employee information like name, employee ID, and department. Now, if we need to add additional attributes such as qualifications, certifications, or employee achievements to this table, creating an extension table would be a suitable solution. This extension table can then be linked to the original 'Employees' table using a common attribute like employee ID. Using an extension table offers several advantages. It helps in maintaining a clean and concise structure of the primary table. It reduces data redundancy by storing less frequently used attributes separately. Moreover, it allows for easy scalability and flexibility in adding or modifying attributes without impacting the main table structure. Extension tables enhance database performance by reducing the size of the primary table and improving data retrieval operations.