Summary

Transactions are SQL Server's basic unit of work. They ensure that a data modification operation is carried out either completely or not at all. Atomicity, consistency, isolation, and durability—the so-called ACID properties—characterize SQL Server transactions and help guard your data against incomplete or lost updates.

The current transaction isolation level (TIL) governs transaction isolation. You set the TIL via the SET TRANSACTION ISOLATION LEVEL command. Each TIL represents a trade-off between concurrency and consistency.