sql With(NoLock),With(ReadPast)

Posted 2020-10-08 zhyue93

sql事务对表的锁及With(NoLock),With(ReadPast)对表的查询结果对比

---------------
create table tmp1
( 
    id int primary key,
    name nvarchar(20)
)

-----------
insert into tmp1(id,name) values(1,\'zhsan1\');
insert into tmp1(id,name) values(2,\'lisi1\');

-------------------------------
select * from tmp1

---

 

更新（Update）语句对数据库加锁

-----------------------------
begin tran tran1
    update tmp1 set name=\'zhsan\' where id=1
-------------------------------
select * from tmp1

查询一直在进行，此时表已经被锁住了

-------------------------------
update tmp1 set name=\'lisi\' where id=2
-------------------------------
select * from tmp1 where id>1

-------------------------------
delete from tmp1 where id=2
-------------------------------
select * from tmp1 where id>1

查询，更新，删除除被锁定的那行数据都能成功，说明被锁住的只有id=1的那一行，对其他行的查询，更新及删除无影响

插入语句

-------------------------------
insert into tmp1(id,name) values(3,\'lisi\')
-------------------------------
select * from tmp1 where id>1

结果执行成功，说明插入不受影响

---

 先将数据库还原为

-----------------------------
begin tran tran1
    update tmp1 set name=\'zhsan\' where id=1

with(readpast)与with(nolock)

-------------------------------
select * from tmp1 with(readpast)

-------------------------------
select * from tmp1 with(nolock)

with(readpast)会忽略被锁住的那一行，with(nolock)不会