Transactions : A transaction is a set of sql statements that are executed as single sql statement,If the statement executes successfully Commit the transaction else Rollbacks on failure.
Usage :
Begin tran insert into dbo.sampletable values('',null,GETDATE(),null) insert into dbo.sampletable values(1,'',null,GETDATE(),null) //Inserting identity value will fail the query. IF @@ERROR<>0 ROLLBACK ELSE COMMIT
In the above code,i am making an insert into an identity column which will fail the query and in turn roll back the transaction and also make a note that none of the rows would be inserted since transaction failed.