Question

我有以下查询。我做的部分

     select for max(Entered_On).....

花费的时间最长。如果我注释掉原因，它会快速运行。

      Select   dlp.ParamID, dp.ParamName   
      from data_LocP  dlp 
      inner join data_In  di on dlp.LocID = di.LocID
      inner join data_Parms dp on dp.ParamID = di.ParamID
      inner join map_Loc ml on ml.LocId =  dlp.LocId
      where di.Entered_On = (select max(Entered_On ) from data_In where LocId = dlp.LocID
      and ParamId = dlp.ParamID)

我想知道是否有一种方法可以优化此查询，因为我获得Max（Entered_On）的部分花费的时间最长。作为一个FYI，我需要将Entered_On作为给定LocId和ParamId的最大日期。

这是一个更加扩展的代码但不提供max：

      select   *  FROM
      (
        SELECT dlp.ParamID, dp.ParamName, dlp.LocID,  ml.LocName , di.Entered_On, (GETUTCDATE() -  dlp.FreqDays) DueDate, dlp.FreqDays,  
        a.CompanyId, a.SiteID, 
          ROW_NUMBER() OVER (PARTITION BY dlp.LocId, dlp.ParamID 
                          ORDER BY di.Entered_On DESC)
             as RowNum            

      from data_LocParams dlp 
      inner join data_Input di on dlp.LocID = di.LocID
      inner join data_Parameters dp on dp.ParamID = di.ParamID
      inner join map_Locations ml on ml.LocId =  dlp.LocId
      left join
     (
       select ml.LocId,ms.CompanyId, ms.SiteId  
       from map_Sites ms 
       join map_WaterSystems mw
       on ms.SiteID = mw.SiteID
       join map_Locations ml
       on ml.SysID = mw.SysID
      ) a 
      on a.LocId = dlp.LocID   
      where   dlp.FreqDays is not null AND dlp.FreqDays <> ''      
   ) as a WHERE a.RowNum = 1 and Entered_On < (GETUTCDATE() -   FreqDays)

Answer 1

尝试使用ROW_NUMBER()代替相关子查询：

SELECT * FROM (
  SELECT   dlp.ParamID, dp.ParamName, 
           ROW_NUMBER() OVER (PARTITION BY dlp.LocId, dlp.ParamID 
                              ORDER BY di.Entered_On) as RowNum
  FROM data_LocP  dlp 
  JOIN data_In  di on dlp.LocID = di.LocID
  JOIN data_Parms dp on dp.ParamID = di.ParamID
  JOIN map_Loc ml on ml.LocId =  dlp.LocId
) WHERE RowNum = 1

如果您有多条记录可以匹配相同的Entered_On值，请使用RANK()代替ROW_NUMBER()。

Answer 2

除了对SQL SELECT的任何更改外，请尝试以Entered_On顺序构建一个DESC的索引。这应该有助于任何需要对Entered_On DESC进行排序或拉出Entered_On的MAX的查询。

CREATE NONCLUSTERED INDEX idx_entered_on ON data_in
(
    LocId, ParamId, Entered_On DESC
)

Answer 3

您说“我需要将Entered_On作为给定LocId和ParamId的最大日期”，但您没有为这些字段指定任何值。类似的东西：

where locId = something
and ParamId = something

主查询和子查询中的

将为您提供您想要的内容，并且可以非常快速地完成。

SQL Optimize查询以获取最大值

3 个答案: