Cassandra Practice Test

The "ALTER TABLE" command in Cassandra is designed to modify the structure of an existing table without impacting its availability or data. This command allows for several important operations such as changing the datatype of a column, adding new columns, dropping existing columns, renaming columns, and updating table properties.

This capability is crucial for maintaining and evolving the database schema to meet changing requirements. For instance, if an application needs to store additional information, new columns can be added seamlessly. Similarly, if the requirements change and a column needs to be renamed for clarity or updates in data types are necessary to accommodate new formats of data, "ALTER TABLE" provides the flexibility needed for these changes.

Other options listed do not accurately reflect the capabilities of the "ALTER TABLE" command. Primary keys cannot be altered without recreating the table, which is a more complex process. Additionally, the command does not deal with removing all data from a table or adjusting cluster configurations, which are managed through different commands and settings in Cassandra. Therefore, the correct answer highlights the comprehensive range of modifications that can be performed on existing tables using the "ALTER TABLE" command.