如何在MySQL中使用表A与自身以一对多关系联接两个表？

Question

我有两张桌子。

“商店”表是一个受众特征表，其中包含以下字段：

ID，ParentID，ConsolidationType

ID是给定商店的唯一标识符。

如果ParentID的ConsolidationType为'Secondary'，则可以为NULL或包含其父存储的ID。

ConsolidationType为NULL，“ Primary”或“ Secondary”。

“销售”表具有以下字段：

StoreID，SalesDate，SalesAmount

StoreID是指Store表中的ID。

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我正在尝试在单个查询的单行中获取给定商店的总合并销售量和个人销售量。 我编写了如下的SQL查询：

SELECT 
Store.ID AS 'Store ID',
SUM(IF(YEAR(main.SalesDate) = 2012 AND QUARTER(main.SalesDate) = 1,main.SalesAmount,0)) AS 'Individual Sales',
SUM(IF(YEAR(main.SalesDate) = 2012 AND QUARTER(main.SalesDate) = 1 AND YEAR(secondaries.SalesDate) = 2012 AND QUARTER(secondaries.SalesDate) = 1,main.SalesAmount + secondaries.SalesAmount,0) AS 'Consolidated Sales'
FROM Store 
LEFT JOIN Sales AS 'main' ON Store.ID = main.StoreID 
LEFT JOIN Sales AS 'secondaries' ON Store.ParentID = secondaries.StoreID 
GROUP BY Store.ID

我不明白为什么这不能按预期工作。 我想念什么？ 我的逻辑怎么了？

Answer 1

问题是您的查询正在生成笛卡尔乘积（类似）结果集。

基本上，对于“次要”中的每个匹配行，“ main”中的一行将重复多次。

要获得所需的结果，只需加入一次sales表，然后在StoreID和ParentID上进行匹配。

要获得Individual Sales ，只能在StoreID匹配的SUM行中包括以下内容：

SELECT Store.ID AS `Store ID`
     , SUM(IF(main.StoreID = Store.ID,
       IF(YEAR(main.SalesDate) = 2012 AND QUARTER(main.SalesDate) = 1,main.SalesAmount,0)
       ,0)) AS `Individual Sales`
     , SUM(
       IF(YEAR(main.SalesDate) = 2012 AND QUARTER(main.SalesDate) = 1,main.SalesAmount,0)
       ) AS `Consolidated Sales`
  FROM Store 
  LEFT JOIN Sales AS `main` ON main.StoreID = Store.ID OR main.StoreID = Store.ParentID
 GROUP BY Store.ID

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更新

我的错。 （DOH！） ParentID在Store表上，而不在Sales表上。

上面的查询不返回指定的结果。 （正在努力。）

我认为您已经有了解决方案...

使用 ParentID列代替 Store表中的 ID列。 当ParentID列为NULL时，我们使用 ID列中的值。

 
 
 
  
  SELECT IFNULL(Store.ParentID,Store.ID) AS `Store ID` , SUM(IF(main.StoreID = Store.ID, IF(YEAR(main.SalesDate) = 2012 AND QUARTER(main.SalesDate) = 1,main.SalesAmount,0) ,0)) AS `Individual Sales` , SUM( IF(YEAR(main.SalesDate) = 2012 AND QUARTER(main.SalesDate) = 1,main.SalesAmount,0) ) AS `Consolidated Sales` FROM Store s LEFT JOIN Sales AS `main` ON main.StoreID = Store.ID OR main.StoreID = Store.ParentID GROUP BY IFNULL(Store.ParentID,Store.ID)
 
  

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此查询返回指定的结果集：

 SELECT t.StoreID AS `Store ID` , SUM(IF(t.source='p', IF(YEAR(t.SalesDate) = 2012 AND QUARTER(t.SalesDate) = 1,t.SalesAmount,0) ,0)) AS `Individual Sales` , SUM( IF(YEAR(t.SalesDate) = 2012 AND QUARTER(t.SalesDate) = 1,t.SalesAmount,0) ) AS `Consolodiated Sales` FROM ( SELECT 'p' AS source , a.StoreID , a.SalesDate , a.SalesAmount FROM Sales a UNION ALL SELECT 's' AS source , s.ParentID , b.SalesDate , b.SalesAmount FROM Sales b JOIN Store s ON s.ID = b.StoreID WHERE s.ParentID IS NOT NULL ) t GROUP BY t.StoreID ORDER BY t.StoreID 

这不是最有效的，内联视图（或“派生表”）按Sales表的大小顺序排列。 将日期上的谓词下推到内联视图中，或在派生表中按月或季度进行汇总，会更有效。

我更可能将“四分之一”作为结果集的一部分返回，以使我可以拉出四分之一以上。

 SELECT t.StoreID AS `Store ID` , t.SalesQuarter , SUM(IF(t.source='p',t.SalesAmount,0)) AS `Individual Sales` , SUM(t.SalesAmount) AS `Consolodiated Sales` FROM ( SELECT 'p' AS source , a.StoreID , ADDDATE(MAKEDATE(YEAR(a.SalesDate),1), INTERVAL FLOOR(MONTH(a.SalesDate)/4) QUARTER) AS SalesQuarter , SUM(a.SalesAmount) AS SalesAmount FROM Sales a -- WHERE a.SalesDate >= '2012-01-01' -- AND a.SalesDate < '2012-04-01' GROUP BY a.StoreID, SalesQuarter UNION ALL SELECT 's' AS source , s.ParentID , ADDDATE(MAKEDATE(YEAR(b.SalesDate),1), INTERVAL FLOOR(MONTH(b.SalesDate)/4) QUARTER) AS SalesQuarter , SUM(b.SalesAmount) AS SalesAmount FROM Sales b JOIN Store s ON s.ID = b.StoreID WHERE s.ParentID IS NOT NULL -- AND a.SalesDate >= '2012-01-01' -- AND a.SalesDate < '2012-04-01' GROUP BY s.ParentID, SalesQuarter ) t GROUP BY t.StoreID, t.SalesQuarter ORDER BY t.StoreID, t.SalesQuarter 

Answer 2

我通常尝试将过滤逻辑保留在WHERE子句中。 您的原始查询可能有太多的JOINS并且在没有孩子的情况下可能无法满足您的期望。 下面的WHERE中的IS NULL检查允许存储没有子项的商店。

SELECT
  s.ID
  , SUM(s.SalesAmount) AS `Individual Sales`
  , SUM(s.SalesAmount) + SUM(c.SalesAmount) AS `Consolidated Sales`
FROM Store AS s
LEFT OUTER JOIN Store AS c ON c.ParentID = s.ID
WHERE YEAR(s.SalesDate) = 2012 AND QUARTER(s.SalesDate) = 1
  AND (c.SalesDate IS NULL OR
    (YEAR(c.SalesDate) = 2012 AND QUARTER(c.SalesDate) = 1))
GROUP BY s.ID