SELECT FOR UPDATE is a SQL command designed to manage concurrent transactional workloads by locking rows identified in a SELECT query until the transaction is committed, thereby preventing transaction conflicts and reducing unnecessary retries. It enhances efficiency by placing concurrent transactions in a queue to be executed sequentially, ensuring smoother processing of contended transactions. However, its implementation and support vary across different SQL databases, with some like MySQL supporting it and others like SQLite opting for different transaction handling methods due to their approach to isolation levels. In databases like CockroachDB, SELECT FOR UPDATE can be used alongside serializable isolation without locking the entire database, supporting performance and consistency simultaneously. Various parameters such as NOWAIT and FOR SHARE modify its behavior, offering different levels of row-locking, but their availability also depends on the specific database system.