相关疑难解决方法(0)

我在MS Sql Server 2008 R2中有一个简单的队列实现.这是队列的本质:

CREATE TABLE ToBeProcessed 
(
    Id BIGINT IDENTITY(1,1) PRIMARY KEY NOT NULL,
    [Priority] INT DEFAULT(100) NOT NULL,
    IsBeingProcessed BIT default (0) NOT NULL,
    SomeData nvarchar(MAX) NOT null
)

我想原子地选择按优先级排序的前n行和IsBeingProcessed为false的id,并更新这些行以表示它们正在被处理.我以为我会使用Update,Top,Output和Order By的组合,但不幸的是你不能在Update语句中使用top和order by.

所以我创建了一个in子句来限制更新,并且子查询按顺序执行(见下文).我的问题是,这整个语句是原子的,还是我需要将它包装在一个事务中？

DECLARE @numberToProcess INT = 2

CREATE TABLE #IdsToProcess
(
    Id BIGINT NOT null
)

UPDATE 
    ToBeProcessed
SET
    ToBeProcessed.IsBeingProcessed = 1
OUTPUT 
    INSERTED.Id 
INTO
    #IdsToProcess   
WHERE
    ToBeProcessed.Id IN 
    (
        SELECT TOP(@numberToProcess) 
            ToBeProcessed.Id 
        FROM 
            ToBeProcessed 
        WHERE
            ToBeProcessed.IsBeingProcessed = 0
        ORDER BY 
            ToBeProcessed.Id, 
            ToBeProcessed.Priority DESC)

SELECT 
    * …