Often there is a need to find records which exist in source table but not in target table.
This can be achieved with simple SQL statement:
SELECT * FROM t1 WHERE NOT EXISTS (SELECT * FROM t2 WHERE t2.Id = t1.Id)
SELECT * FROM t1 LEFT OUTER JOIN t2 ON t1.Id = t2.Id WHERE t2.Id IS NULL
This works not only for SQL Server, but also for many other databases.