在大型表上优化多重连接查询

Question

我正在为现有应用程序编写一个附加项，并且需要为各种事务类型获取数量总和。每个事务类型都有一套独特的标准ta_code，ta_type和ta_asc

下查询并返回所需的信息，但最终，trans表中有大约500万条记录，因此需要4分钟，运行

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 

每个连接似乎都会增加无效率，但即使单独运行，每个连接选择也需要10秒才能运行。我们只能读取这个数据库，所以不能以任何方式改变它。

如果有人能够建议一种可以更有效地实现这一点的方法或结构，我将不胜感激。

Answer 1

这可能是值得一试：删除所有“左连接”的条款，并计算有条件的总和，这样的事情：

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

这里有一些事情，我会尝试：

1. 在itmCode列
2. 添加索引移动INNER JOIN项目正如我在i.code = t.itmcode作为第一个加入
3. 将“SELECT sum（qty）as sQty，itmcode FROM trans WHERE site = 127 AND ta_code ='12' GROUP BY itmcode”用作临时表，然后在其他左连接中将其用于adda ta_type，因为您重复此操作不必要地在每个左连接中查询。

我也总是建议学习和使用MS SQL配置文件，如果您使用的是MS SQL。