sql server中没有锁意味着什么 [英] No Lock in sql server means what

问题描述

在SQL Server中(Nolock)的含义是什么，请举一个例子来解释吗?

What is the meaning of the (Nolock) in sql server and pls explain with an example ?

推荐答案

您已经给出了很多很好的链接，但是我会建议也阅读这篇文章当使用NOLOCK时应该考虑什么使用提示 [ ^ ]

You have given many good links already, but I would suggest also going through this article What should be considered when NOLOCK hint is used[^]

(NOLOCK)等同于使用READ UNCOMMITED 作为事务隔离级别.因此，您有读取未提交的行并随后回滚的风险，即数据永远不会进入数据库.因此，虽然它可以防止读取因其他操作而陷入僵局.

WITH (NOLOCK) is the equivalent of using READ UNCOMMITED as a transaction isolation level. So, you stand the risk of reading an uncommitted row that is subsequently rolled back, i.e. data never made it into the database. So, while it can prevent reads being deadlocked by other operations.

SELECT * FROM Employee WITH (READUNCOMMITTED)

这与
一样

this is same as

SELECT * FROM Employee  WITH NOLOCK

NOLOCK和READUNCOMMITED提示仅允许用于SELECT语句.如果我们尝试将其用于UPDATE, DELETE or INSERT，则会收到错误消息.

查看此链接以获取示例.

http://www.mssqltips.com/sqlservertip/2470/understanding-the -sql-server-nolock-hint/ [

The NOLOCK and READUNCOMMITED hints are only allowed with SELECT statements. If we try to use this for an UPDATE, DELETE or INSERT we will get an error.

Check this link for an example.

http://www.mssqltips.com/sqlservertip/2470/understanding-the-sql-server-nolock-hint/[^]

使用NOLOCK查询提示时，您告诉存储引擎您要访问数据，无论是否数据是否被另一个进程锁定.
参考链接:- WITH(NOLOCK)到底是什么意思 [ ^ ]

When you use the NOLOCK query hint you are telling the storage engine that you want to access the data no matter if the data is locked by another process or not.
Reference Link :- What does WITH (NOLOCK) actually mean[^]

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