Listing 1: [Need a Caption Here]
/* Connection 1:
For full snapshot isolation, we must set it at the session level, because the database option only enables 
it, it doesn't actually turn it on. */

USE testdb
SET TRANSACTION ISOLATION LEVEL SNAPSHOT
BEGIN TRAN
SELECT A FROM t WHERE K =1 

--SQL Server returns 5.

-- Connection 2:
USE testdb
BEGIN TRAN
SELECT A FROM t WHERE K =1 

--SQL Server returns 5.

-- Connection 3: 
USE testdb
UPDATE t SET A = 9 WHERE K = 1	

--Connection 3 performs the update and auto commits the transaction.

-- Back to Connection 1
SELECT A FROM t WHERE K =1 

-- SQL Server still returns 5.

-- Back to Connection 2
SELECT A FROM t WHERE K =1 

-- SQL Server returns 9.

/* Back to Connection 3
 You can start another update on Connection 3 before Connection 1 or 2 commits. */

UPDATE t SET A = 11 WHERE K = 1