Unique constraints and indexes in databases, such as MySQL, are essential tools for maintaining data integrity by preventing duplicate entries. Beyond their basic functionality, unique indexes enable efficient data manipulation through SQL commands like INSERT ... ON DUPLICATE KEY UPDATE and INSERT IGNORE, which help manage concurrency and minimize race conditions in scenarios like ad impression tracking. These commands streamline processes by allowing single-step operations that handle potential duplicates, enhancing performance and reliability. Additionally, unique indexes can include nullable values, where NULL entries are not considered duplicates, allowing flexibility in database design. Overall, unique indexes, when combined with advanced SQL operations, offer powerful solutions for maintaining data consistency and optimizing database performance.