SQL Server查詢優化

Question

我繼承了這個在SQL Server中爲分頁設計的地獄般的查詢。

它只能獲得25條記錄，但根據SQL Profiler，它可以讀取8091條記錄，寫入208條記錄，耗時74毫秒。寧願它快一點。 ORDER BY列deployDate上有一個索引。

任何人有任何想法如何優化它？

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

我處於與相同類型的查詢類似的位置。這裏有一些提示：

• 看看查詢計劃，以確保您有正確的索引。
• 我不確定MSSQL是否優化了DATEDIFF（），但是如果不是，您可以預先計算閾值日期並將其轉換爲BETWEEN子句。
• 如果您不需要按照您的ROW_NUMBER（）子句中的所有列進行排序，請刪除它們。這可能允許您在更簡單的查詢上執行分頁，然後只需獲取您要返回的25行所需的額外數據。

而且，改寫兩個LEFT OUTER JOINs這樣的：

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

這將使查詢優化器表現更好一點。