Question

我有一个主表和一个子表。主表是零件的主列表，子表是构建零件所需的集合零件。每个子部分都通过ParentID链接到其父部分。

零件或“子零件”有一个ChildID，它指向主要零件清单中它自己的条目。我们使用此链接来获取价格，因为在子表中仅存储ID。

如果我想将构成每个父部件的所有子部件的总成本相加。我将如何构造该查询？

总成本应该是一个计算字段，该字段将选择子表中所有具有ID的ParentID ==的部件，并将其总价*数量相加。

这是我到目前为止所拥有的：

//This Query Doesnt work. Just returns 0.
SELECT SUM(PricePer * Qty)
    FROM sub inner join main on sub.ChildPID = main.ID where sub.ParentPID = main.ID

//This query will work, where the main.ID is entered manually. but I cant do this
SELECT SUM(PricePer * Qty)
    FROM sub inner join main on sub.ChildPID = main.ID where sub.ParentPID = 1

示例：

主表

ID | Name | TotalCost | PricePer 

1    Part1  10.00       14.00**   SELECTED

2    Part2  0.00        6.00

3    Part3  0.00        2.00

子表

ParentID | ChildID | Name | Qty

1          2         Part2  1

1          3         Part3  2

Answer 1

您不应该在左连接中使用where子句，否则会作为内部连接
并且如果您想将结果与上层查询联系起来..您对总和进行分组，并按与上层查询相关的关键字进行分组

您可以直接根据合并的结果执行更新，例如：

update main  
inner join  (
  SELECT  main.ID, SUM(main.PricePer) total_x_id
  FROM sub 
  INNER  join main on sub.ChildID = main.ID
  group by main.ID 
) t on t.id = main.id 
set total = t.total_x_id

如果您只需要选择，则

 SELECT  main.ID, SUM(main.PricePer) total_x_id
 FROM sub 
 INNER  join main on sub.ChildID = main.ID
 group by main.ID

您可以使用

作为连接在上层查询中获得结果

select  maint.id, ifnull(t.total_x_id ,0)
from main 
left  join (
  SELECT  ChildID.ID as ID, SUM(main.PricePer) total_x_id
  FROM sub 
  group by ChildID.ID 
) t  on t.ID = main.id

Answer 2

这是一个级别的选择：

SELECT m.priceper + SUM(s1.qty * m2.priceper) AS priceper
FROM main m
LEFT JOIN sub s1 ON (m.id = s1.parentid)
LEFT JOIN main m2 ON (m2.id = s1.childid)
-- WHERE m.id = 1
GROUP BY m.id;

对于2个级别，将是这样的（我无法尝试，可能需要一些修复）：

SELECT m1.id, m1.priceper + IFNULL(SUM(s1.qty * g2.priceper),0) AS priceper
FROM main m1
LEFT JOIN sub s1 ON (m1.id = s1.parentid)
LEFT JOIN (
    SELECT m2.id, m2.priceper + IFNULL(SUM(s2.qty * g2.priceper),0) AS priceper
    FROM main m2
    LEFT JOIN sub s2 ON (m2.id = s2.parentid)
    LEFT JOIN main g2 ON (g2.id = s2.childid)
    GROUP BY m2.id)
g2 ON (g2.id = s1.childid)
-- WHERE m1.id = 1
GROUP BY m1.id;

要向下钻取，您需要用g3等的子查询替换主表...

SELECT m1.id, m1.priceper + IFNULL(SUM(s1.qty * g2.priceper),0) AS priceper
FROM main m1
LEFT JOIN sub s1 ON (m1.id = s1.parentid)
LEFT JOIN (
    SELECT m2.id, m2.priceper + IFNULL(SUM(s2.qty * g2.priceper),0) AS priceper
    FROM main m2
    LEFT JOIN sub s2 ON (m2.id = s2.parentid)
    LEFT JOIN (
        SELECT m3.id, m3.priceper + IFNULL(SUM(s3.qty * g3.priceper),0) AS priceper
        FROM main m3
        LEFT JOIN sub s3 ON (m3.id = s3.parentid)
        LEFT JOIN main g3 ON (g3.id = s3.childid)
        GROUP BY m3.id) g2 
        ON (g2.id = s2.childid)
    GROUP BY m2.id) g2 
    ON (g2.id = s1.childid)
-- WHERE m1.id = 1
GROUP BY m1.id;

对于4个级别，它看起来像这样：

SELECT m1.id, m1.priceper + IFNULL(SUM(s1.qty * g2.priceper),0) AS priceper
FROM main m1
LEFT JOIN sub s1 ON (m1.id = s1.parentid)
LEFT JOIN (
    SELECT m2.id, m2.priceper + IFNULL(SUM(s2.qty * g2.priceper),0) AS priceper
    FROM main m2
    LEFT JOIN sub s2 ON (m2.id = s2.parentid)
    LEFT JOIN (
        SELECT m3.id, m3.priceper + IFNULL(SUM(s3.qty * g3.priceper),0) AS priceper
        FROM main m3
        LEFT JOIN sub s3 ON (m3.id = s3.parentid)
        LEFT JOIN (
            SELECT m4.id, m4.priceper + IFNULL(SUM(s4.qty * g4.priceper),0) AS priceper
            FROM main m4
            LEFT JOIN sub s4 ON (m4.id = s4.parentid)
            LEFT JOIN main g4 ON (g4.id = s4.childid)
            GROUP BY m4.id) g3
        ON (g3.id = s3.childid)
        GROUP BY m3.id) g2 
        ON (g2.id = s2.childid)
    GROUP BY m2.id) g2 
    ON (g2.id = s1.childid)
-- WHERE m1.id = 1
GROUP BY m1.id;

Answer 3

这变得比我想象的要复杂。也许这是我的错，因为我不清楚。这是我发现可行的解决方案。

Select *, ifnull((SELECT SUM(main.PricePer * Qty)
    FROM sub inner join main on sub.ChildID = main.ID where sub.ParentID = main1.PID), 0) from main as main1

如何从相关表中求和

3 个答案: