If no quorum is reached in a MySQL InnoDB Cluster, the cluster cannot process transactions until a majority of nodes agree on the promotion of a new primary, ensuring data consistency and avoiding split- brain scenarios.

The DROP USER command is used to remove a user account from MySQL entirely. It removes the user and their privileges from the system.

The UNIQUE constraint ensures that all values in the column are unique across all rows in the table, preventing duplicate entries.

MySQL Enterprise Monitor provides a visual dashboard that helps administrators track the health and performance of MySQL databases, offering real-time monitoring and optimization suggestions.

The default replication mode in MySQL is asynchronous replication, where the primary server commits changes without waiting for confirmation from the replicas.