Sql server select语句（在原始示例中）当您在事务中运行它时，将显示查询2可以在提交之前对查询1的数据执行可重复读取。在两个更新查询之前添加select*from locks where lockname='a'，您将发现您可以在不应该读取数据的时候读取数据。我文

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select语句（在原始示例中）当您在事务中运行它时，将显示查询2可以在提交之前对查询1的数据执行可重复读取。在两个更新查询之前添加

select*from locks where lockname='a'

，您将发现您可以在不应该读取数据的时候读取数据。我文章的全部要点是，在提交数据之前，我不想读取数据，这不应阻止我读取未包含在该读取中的未读取行。

output inserted.

是选择项。除此之外，

从lockname='A'

所执行操作的锁中进行选择：更新后的块。我以前见过一些人不听劝告，但你把标准定得太高了。。。

begin transaction
select lockname from locks  where lockname='A'
update Locks Set locked=1 where lockname='A'

begin transaction
select lockname from locks  where lockname='A'

CREATE TABLE [dbo].[Locks]( 
    [LockName] [varchar](50) NOT NULL, 
    [Locked] [bit] NOT NULL, 
    CONSTRAINT [PK_Locks] PRIMARY KEY CLUSTERED  ([LockName]));
GO    

insert into Locks (LockName, Locked) values ('A', 0);
insert into Locks (LockName, Locked) values ('B', 0);
GO

begin transaction
update Locks 
  set Locked=1 
  output inserted.*
  where LockName = 'A';

begin transaction
update Locks 
  set Locked=1 
  output inserted.*
  where LockName = 'B';

begin transaction 
select lockname from locks  where lockname='A' 
update Locks Set locked=1 where lockname='A'

begin transaction 
update Locks 
 Set locked=1 
 output inserted.*
 where lockname='A'

create table Resources (
   id int identity(1,1) not null,
   enqueue_time datetime not null default getutcdate(),
   is_processing bit not null default 0,
   payload xml);

create clustered index cdxResources on Resources 
  (is_processing, enqueue_time);
go   

-- enqueue:
insert into Resources (payload) values ('<do>This</do>');
insert into Resources (payload) values ('<do>That</do>');
insert into Resources (payload) values ('<do>Something</do>');
insert into Resources (payload) values ('<do>Anything</do>');

--dequeue
begin transaction;
with cte as (
  select top(1) *
  from Resources with(readpast)
  where is_processing = 0
  order by enqueue_time)
update cte
  set is_processing = 1
  output inserted.*;