左连接后 table 中的重复记录

Question

我有三个table。

“部门”table: department_name, department_id.

Table "LowPrice": departmend_id, product_name, 购买, 出售, 价格。

Table“基本”：departmend_id、product_name、购买、出售、价格。

在table的“基本”和“低”中，一个部门可以有多个记录。

这些table之间没有关系。我想开发一个查询，根据部门 table 中的部门编号对 Low 和 Basic table 中的记录进行分组。分组时，每个部门的“基本”和“低价”table销售和采购商品的成本相加。

我的查询代码：

    SELECT Departments.departmend_id, 
    Sum([Basic]![purchased] [Basic]![price]) AS PurchasedBasic 
    Sum([Basic]![sold] [Basic]![price]) AS SoldBasic, 
    Sum([Basic]![purchased] [Basic]![price]) - Sum([Basic]![sold][Basic]![price]) AS DiffBasic, 
    Sum([LowPrice]![purchased] [LowPrice]![price]) AS PurchasedLowPrice, 
    Sum([LowPrice]![sold] [LowPrice]![price]) AS SoldLowPrice, 
    Sum([LowPrice]![purchased] [LowPrice]![price]) - Sum([LowPrice]![sold] [LowPrice]![price]) AS DiffLowPrice
    FROM (Departments LEFT JOIN Basic ON Departments.departmend_id = Basic.departmend_id) LEFT JOIN LowPrice ON Departments.departmend_id = LowPrice.departmend_id
    GROUPBY Departments.departmend_id;

但现在只有那些只有一个 table 中有记录的部门才被正确统计。如果两个 table 中有一个部门的记录，则它们的数量将相乘，查询将给出不正确的结果。

请告诉我我的查询需要更改什么。

Answer 1

考虑将 LowPrice 和 BasicPrice 合并为一个 table，因为它们在质量上包含相同的信息。只需添加一个类型字段来指定低价和基本价格记录。

Make-Table查询(待运行一次)

SELECT p.*
INTO Prices
FROM
   (SELECT b.department_id,
           b.product_name,
           b.purchased,
           b.sold, 
           b.price,
           'Basic Price' AS type
    FROM BasicPrice b

    UNION ALL

    SELECT l.department_id,
           l.product_name,
           l.purchased,
           l.sold, 
           l.price,
           'Low Price' AS type
    FROM LowPrice l
   ) p

一旦您正确规范化了这两个关系以提高存储效率，运行条件聚合。下面使用 table 别名和 MS Access 支持的计算列。

条件聚合查询

SELECT d.departmend_id, 
       d.department_name,
       SUM(IIF(p.Type = 'Basic Price', p.[purchased] * p.[price], NULL)) AS PurchasedBasic,
       SUM(IIF(p.Type = 'Basic Price', p.[sold] * p.[price], NULL)) AS SoldBasic, 
       [PurchasedBasic] - [SoldBasic] AS DiffBasic, 

       SUM(IIF(p.Type = 'Low Price', p.[purchased] * p.[price], NULL)) AS PurchasedLowPrice, 
       SUM(IIF(p.Type = 'Low Price', p.[sold] * p.[price], NULL)) AS SoldLowPrice, 
       [PurchasedLowPrice] - [SoldLowPrice] AS DiffLowPrice

FROM Departments d
LEFT JOIN Prices p ON d.departmend_id = p.departmend_id

GROUP BY d.departmend_id,
         d.department_name;

左连接后 table 中的重复记录

Duplicate records in table after left join

sql

ms-access