Example
SQL Server 2008 R2
SET TRANSACTION ISOLATION LEVEL SNAPSHOT
Specifies that data read by any statement in a transaction will be the transactionally consistent version of the data that existed at the start of the transaction, i.e., it will only read data that has been committed prior to the transaction starting.
SNAPSHOT transactions do not request or cause any locks on the data that is being read, as it is only reading the version (or snapshot) of the data that existed at the time the transaction began.
A transaction running in SNAPSHOT isolation level read only its own data changes while it is running. For example, a transaction could update some rows and then read the updated rows, but that change will only be visible to the current transaction until it is committed.
Note: The ALLOW_SNAPSHOT_ISOLATION database option must be set to ON before the SNAPSHOT isolation level can be used.
