A deadlock occurs when two or more operations wait for resources held by each other and none of them can continue. SQL Server detects this situation, selects one transaction as the victim and rolls it back.

One common reason for deadlocks is accessing resources in different orders. If one transaction locks table A and then table B, while another locks table B and then table A, the risk of deadlock increases.

Keeping transactions short is an effective prevention strategy. Avoid user interaction, long calculations or unnecessary delays inside transactions. Database work should be completed as quickly as possible.

Proper indexing can also reduce locking problems. Without useful indexes, SQL Server may lock more rows or pages than necessary, increasing the chance of conflicts.

Deadlocks may not be completely eliminated, but their impact can be reduced with good transaction design, consistent resource access order, proper indexes and retry logic in the application.