----臟讀----
--事務1--(1)
use pubs
begin transaction
update jobs set job_desc = 'ACCP1' 
where job_id = 1

rollback transaction
commit transaction


----不可重復讀----
--事務1(1,3)隱性事務
use pubs
set implicit_transactions on--(只執(zhí)行1次)
select * from jobs where job_id = 1

rollback transaction
select @@trancount


----幻影讀----
--事務1(1)
set implicit_transactions on--(只執(zhí)行1次)
select * from jobs where job_desc = 'accp'
--(3)
select * from jobs where job_desc = 'accp'

rollback transaction
----以上為事務缺陷----



----事務的隔離級別----
--隔離級別3：Repeatable Read  可重復讀
	  --可以防止臟讀和不可重復讀。
--事務1：
--設置為默認級別(任何事務類型都不能更新)

use pubs
set transaction isolation level Repeatable Read 
set implicit_transactions on--(只執(zhí)行1次)
--(1)
select * from jobs where job_id = 1

--(2)
select * from jobs where job_id = 1

rollback transaction



--4、Serializable     可串行讀(連續(xù)的)
--演示隔離級別3不能阻止添加數據
set transaction isolation level Repeatable Read 
set implicit_transactions on--(只執(zhí)行1次)
--(1)
select * from jobs


--升高隔離級別4
set transaction isolation level Serializable 
set implicit_transactions on--(只執(zhí)行1次)
--(1)
select * from jobs

commit
rollback