剔除异常值后在SQL中取平均值

我有一个通用的日志表,可以附加到进程及其结果。我使用流程性能视图获得平均时间:

WITH    Events
          AS (
              SELECT    PR.DATA_DT_ID
                       ,P.ProcessID
                       ,P.ProcessName
                       ,PL.GUID
                       ,PL.EventText
                       ,PL.EventTime
              FROM      MISProcess.ProcessResults AS PR
              INNER JOIN MISProcess.ProcessResultTypes AS PRT
                        ON PRT.ResultTypeID = PR.ResultTypeID
                           AND PRT.IsCompleteForTiming = 1
              INNER JOIN MISProcess.Process AS P
                        ON P.ProcessID = PR.ProcessID
              INNER JOIN MISProcess.ProcessLog AS PL
                        ON PL.BatchRunID = PR.BatchRunID
                           AND PL.ProcessID = P.ProcessID
                           AND [GUID] IS NOT NULL
                           AND (
                                PL.EventText LIKE 'Process Starting:%'
                                OR PL.EventText LIKE 'Process Complete:%'
                               )
             )
SELECT  Start.DATA_DT_ID
       ,Start.ProcessName
       ,AVG(DATEDIFF(SECOND, Start.EventTime, Finish.EventTime)) AS AvgDurationSeconds
       ,COUNT(*) AS NumRuns
FROM    Events AS Start
INNER JOIN Events AS Finish
        ON Start.EventText LIKE 'Process Starting:%'
           AND Finish.EventText LIKE 'Process Complete:%'
           AND Start.DATA_DT_ID = Finish.DATA_DT_ID
           AND Start.ProcessID = Finish.ProcessID
           AND Start.GUID = Finish.GUID
GROUP BY Start.DATA_DT_ID
       ,Start.ProcessName

现在我可以过滤掉这一点来消除以前几个月的运行,所以一个进程的平均性能只能在过去3个月内得到,比如说。

当由于性能或调试不好而出现异常值时,问题就出现了,进程在0秒内完成。

我想以某种方式自动消除任何异常值。

VAR() 或 STDEV() 聚合函数有效吗?