提高性能的替代方案？使用带 Top1 和顺序的外部应用

Question

感谢上一个问题中的所有帮助，我的项目取得了很大进展，甚至学到了很多东西。我希望能在我目前面临的性能下降问题上获得一些帮助。基本上，我们正在使用一个数据库，该数据库有一个名为“AlertHistory”的表，并且该表没有被索引（我知道，...）。我的目标是获取 AlertHistory 表中与当前 alertid 相关的最新条目。我的想法是使用外连接，但这对我们的生产服务器造成了巨大的性能损失（执行时间从大约 20 秒到大约 3 分钟）。

SELECT
    AllAlerts.AlertID as AlertID,
    Queues.QueueID as QueueID,
    Queues.QueueName as QueueName,
    AllAlerts.ConnectorID as ConnectorID,
    AllAlerts.DeviceID as DeviceID,
    AllAlerts.SituationMessage as Summary,
    AllAlerts.AlertDetail as Detail,
    AllAlerts.Acknowledged as Acknowledged,
    "AcknowledgedBy" =
        CASE
            WHEN AllAlerts.Acknowledged = '1' THEN History.CreatedBy
            WHEN AllAlerts.Acknowledged = '0' THEN ' '
        END,
    AllAlerts.AssignedTo as AssignedTo,
    AllAlerts.ReportedTime as CreatedTime,
    AllAlerts.ClearedTime as ClearedTime

from 
    [ISG_SOI ].[dbo].[Alerts] as AllAlerts

    inner join [ISG_SOI ].[dbo].[AlertQueueAssignments] as QA 
        on QA.[AlertID] = AllAlerts.[AlertID]
    inner join [ISG_SOI ].[dbo].[AlertQueues] AS Queues 
        on Queues.[QueueID] = QA.[QueueID]

    outer apply (
        select top 1 History.CreatedBy 
        from [ISG_SOI ].[dbo].[AlertHistory] as History
        where History.ColumnName = '73549' and History.AlertID = AllAlerts.AlertID
        order by History.CreatedTime DESC
    ) as History

where Queues.QueueName = 'OCC'

只是为了解释应用，ColumnName 是我需要获取的静态列。此数据库使用整数标识符 73549。当然我可以使用“声明”并声明一个变量，但我们的实现软件不支持 (BOXI)。

Answer 1

值得一试的选择...

（尝试让 SQL Server 对数据进行一次排序，然后查询它，而不使用临时表或索引真实表。）

inner join [ISG_SOI ].[dbo].[AlertQueueAssignments] as QA 
    on QA.[AlertID] = AllAlerts.[AlertID]
inner join [ISG_SOI ].[dbo].[AlertQueues] AS Queues 
    on Queues.[QueueID] = QA.[QueueID]
inner join
(
    SELECT
        ROW_NUMBER() OVER (PARTITION BY AlertID ORDER BY CreatedTime DESC) AS CreatedOrdinal,
        *
    FROM
        [ISG_SOI ].[dbo].[AlertHistory]
    WHERE
        ColumnName = '73549'
)
    AS History
        ON  History.AlertID        = AllAlerts.AlertID
        AND History.CreatedOrdinal = 1

Answer 2

inner join 
(
    select History.AlertID, max(History.CreatedBy) as CreatedBy
    from [ISG_SOI ].[dbo].[AlertHistory] as History
    where History.ColumnName = '73549'
    group by History.AlertID
) as History
  on History.AlertID  = AllAlerts.AlertID  

您甚至可能想尝试加入提示
哈希或合并应该强制它只被评估一次
[高级查询调优概念][1]

下一步是使用该查询创建#temp。
在 AlertID 上声明 PK，因为查询优化器可以使用该信息。

Answer 3

感谢@MatBailie 和@Blam 提供的帮助，这确实有助于改进查询：

    SELECT
    AllAlerts.AlertID as AlertID,
    Queues.QueueID as QueueID,
    Queues.QueueName as QueueName,
    AllAlerts.ConnectorID as ConnectorID,
    AllAlerts.DeviceID as DeviceID,
    AllAlerts.SituationMessage as Summary,
    AllAlerts.AlertDetail as Detail,
    AllAlerts.Acknowledged as Acknowledged,
    "AcknowledgedBy" = 
        CASE
            WHEN AllAlerts.Acknowledged = '1' THEN ISNULL(History.CreatedBy, '')
            WHEN AllAlerts.Acknowledged = '0' THEN ' '
        END,
    AllAlerts.AssignedTo as AssignedTo,
    DATEADD(HOUR, -5, AllAlerts.ReportedTime) as CreatedTime,
    DATEADD(HOUR, -5, AllAlerts.ClearedTime) as ClearedTime,
    AllAlerts.SvcDeskTicket as TicketID

from 
    [ISG_SOI ].[dbo].[Alerts] as AllAlerts

    inner join [ISG_SOI ].[dbo].[AlertQueueAssignments] as QA 
        on QA.[AlertID] = AllAlerts.[AlertID]
    inner join [ISG_SOI ].[dbo].[AlertQueues] AS Queues 
        on Queues.[QueueID] = QA.[QueueID]

    left join 
    (
        select History.AlertID, max(History.CreatedBy) as CreatedBy
          from [ISG_SOI ].[dbo].[AlertHistory] as History
         where History.ColumnName = '73549'
           and History.Currentvalue = 'true'
         group by History.AlertID
    ) as History
      on History.AlertID  = AllAlerts.AlertID 

where Queues.QueueName = 'OCC'