--------------- 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
sql With(NoLock),With(ReadPast)
原文：http://www.cnblogs.com/zhyue93/p/sql_nolock_readpast.html