SQL Server查詢優化

Question

我繼承了這個專為SQL Server分頁設計的地獄查詢。

它僅獲得25條記錄，但是根據SQL Profiler的數據，它執行8091次讀取，208次寫入並花費74毫秒。 希望它快一點。 ORDER BY列deployDate上有一個索引。

有人對如何優化它有任何想法嗎？

SELECT TOP 25 
    textObjectPK, textObjectID, title, articleCredit, mediaCredit,
    commentingAllowed,deployDate, 
    container, mediaID, mediaAlign, fileName AS fileName, fileName_wide AS fileName_wide, 
    width AS width, height AS height,title AS mediaTitle, extension AS extension, 
    embedCode AS embedCode, jsArgs as jsArgs, description as description, commentThreadID,
    totalRows = Count(*) OVER()
 FROM
    (SELECT 
        ROW_NUMBER() OVER (ORDER BY textObjects.deployDate DESC) AS RowNumber,
        textObjects.textObjectPK, textObjects.textObjectID, textObjects.title,  
        textObjects.commentingAllowed, textObjects.credit AS articleCredit, 
        textObjects.deployDate, 
        containers.container, containers.mediaID, containers.mediaAlign, 
        media.fileName AS fileName, media.fileName_wide AS fileName_wide, 
        media.width AS width, media.height AS height, media.credit AS mediaCredit, 
        media.title AS mediaTitle, media.extension AS extension, 
        mediaTypes.embedCode AS embedCode, media.jsArgs as jsArgs, 
        media.description as description, commentThreadID,
        TotalRows = COUNT(*) OVER ()
     FROM textObjects WITH (NOLOCK) 
     INNER JOIN containers WITH (NOLOCK) 
                ON containers.textObjectPK = textObjects.textObjectPK 
                AND (containers.containerOrder = 0 or containers.containerOrder = 1)
     INNER JOIN LUTextObjectTextObjectGroup tog WITH (NOLOCK)
                ON textObjects.textObjectPK = tog.textObjectPK
                AND tog.textObjectGroupID in (3)
     LEFT OUTER JOIN media WITH (NOLOCK) 
                ON containers.mediaID = media.mediaID 
     LEFT OUTER JOIN mediaTypes WITH (NOLOCK) 
                ON media.mediaTypeID = mediaTypes.mediaTypeID
     WHERE (((version = 1)   
              AND (textObjects.textObjectTypeID in (6))  
       AND (DATEDIFF(minute, deployDate, GETDATE()) >= 0) 
       AND (DATEDIFF(minute, expireDate, GETDATE()) <= 0))
       OR  ( (version = 1) AND (textObjects.textObjectTypeID in (6))  
       AND (DATEDIFF(minute, deployDate, GETDATE()) >= 0) 
       AND (expireDate IS NULL))) 
       AND deployEnglish = 1
       ) tmpInlineView
  WHERE RowNumber >= 51
  ORDER BY deployDate DESC 

Answer 1

我處於與相同查詢相似的位置。 這里有一些提示：

• 查看查詢計划以確保您具有正確的索引。
• 我不確定MSSQL是否圍繞DATEDIFF（）進行優化，但是如果不是，則可以預先計算閾值日期並將其轉換為BETWEEN子句。
• 如果您不需要按ROW_NUMBER（）子句中的所有這些列進行排序，請除去它們。 這可能使您可以對一個簡單得多的查詢進行分頁，然后僅獲取要返回的25行所需的額外數據。

另外，像這樣重寫兩個LEFT OUTER JOINs ：

LEFT OUTER JOIN 
(
    media WITH (NOLOCK) 
        LEFT OUTER JOIN mediaTypes WITH (NOLOCK) 
             ON media.mediaTypeID = mediaTypes.mediaTypeID
)
    ON containers.mediaID = media.mediaID 

這應該使查詢優化器的性能更好一些。