在大型表上優化多重連接查詢

Question

我正在爲現有應用程序編寫一個附加項，並且需要爲各種事務類型獲取數量總和。每個事務類型都有一套獨特的標準ta_code，ta_type和ta_asc

下查詢並返回所需的信息，但最終，trans表中有大約500萬條記錄，因此需要4分鐘，運行

SELECT t.qty AS tQty, sQty, rQty, mQty, lQty, aQty, xQty, t.itmcode 
FROM trans AS t 
LEFT JOIN 
    (
     SELECT sum(qty) as sQty, itmcode 
     FROM trans 
     WHERE 
      site = 127 
      AND ta_code = '12' 
     GROUP BY itmcode 
    )as tblS ON tblS.itmcode = t.itmcode 
LEFT JOIN 
    (
     SELECT sum(qty) as rQty, itmcode 
     FROM trans 
     WHERE 
      site = 127 
      AND ta_code = '12' AND ta_type = '1' 
     GROUP BY itmcode 
    )as tblR ON tblR.itmcode = t.itmcode 
LEFT JOIN 
    (
     SELECT sum(qty) as mQty, itmcode 
     FROM trans 
     WHERE 
      site = 127 
      AND ta_code = '15' AND ta_type = '4' 
     GROUP BY itmcode 
    )as tblM ON tblM.itmcode = t.itmcode 
LEFT JOIN 
    (
     SELECT sum(qty) as lQty, itmcode 
     FROM trans 
     WHERE 
      site = 127 
      AND ta_asc = '147' 
     GROUP BY itmcode 
    )as tblL ON tblL.itmcode = t.itmcode 
LEFT JOIN 
    (
     SELECT sum(qty) as aQty, itmcode 
     FROM trans 
     WHERE 
      site = 127 
      AND ta_asc = '155' 
     GROUP BY itmcode 
    )as tblA ON tblA.itmcode = t.itmcode 
LEFT JOIN 
    (
     SELECT sum(qty) as xQty, itmcode 
     FROM trans 
     WHERE 
      site = 127 
      AND ta_asc = '155' AND ta_code = '15' AND ta_type = '4' 
     GROUP BY itmcode 
    )as tblX ON tblX.itmcode = t.itmcode     
INNER JOIN item AS i ON i.code = t.itmcode  
WHERE t.site = 127 
GROUP BY itmcode 

每個連接似乎都會增加無效率，但即使單獨運行，每個連接選擇也需要10秒才能運行。我們只能讀取這個數據庫，所以不能以任何方式改變它。

如果有人能夠建議一種可以更有效地實現這一點的方法或結構，我將不勝感激。

Answer 1

這可能是值得一試：刪除所有「左連接」的條款，並計算有條件的總和，這樣的事情：

SELECT 
    ISNULL(SUM(CASE WHEN ta_code = '12' and ta_type='1' THEN Qty ELSE 0 END), 0) as rQty, 
    ISNULL(SUM(CASE WHEN ta_code = '15' and ta_type='4' THEN Qty ELSE 0 END), 0) as mQty 

    FROM trans AS t 

    WHERE t.Site = 127 
    GROUP BY itmcode 

Answer 2

這裏有一些事情，我會嘗試：

1. 在itmCode列
2. 添加索引移動INNER JOIN項目正如我在i.code = t.itmcode作爲第一個加入
3. 將「SELECT sum（qty）as sQty，itmcode FROM trans WHERE site = 127 AND ta_code ='12' GROUP BY itmcode」用作臨時表，然後在其他左連接中將其用於adda ta_type，因爲您重複此操作不必要地在每個左連接中查詢。

我也總是建議學習和使用MS SQL配置文件，如果您使用的是MS SQL。