mysql - 合并两个表而不使用 mysql 中的连接？

Question

我尝试合并两个不同表中的值，但没有成功。第一个显示的和我想要的一样，但第二个每次都只显示第一行。

Select * From (Select date as Date, Sum(qty) as qtySum, Sum(weight) 
as weightSum From stock_list Group by date) as A,
(Select Sum(weight) as weightSum,Count(barcode)
as barcodeCount From selected_items Group by date) as B Group by date;

这是我得到的输出。

These is my selected_items table.

这是我的库存 list 。

我的两个查询都是单独工作的，只有当我尝试将它们一起运行时我才会得到正确的输出，这给第二个查询带来了问题。任何人都可以指出我的错误或告诉我更好的方法来做到这一点。 这就是我的最终目标

Answer 1

第一个问题是您在子查询 B 中按日期分组，但您没有选择它，因此您的结果集可能类似于:

weightSum       barcodeCount
---------------------------
26              8
9               14
4               7

这是 3 个日期的结果，但您不知道哪一行指的是哪个日期。

您的下一个问题是您正在使用交叉连接，因为您的两个查询之间没有链接，这意味着如果您的第一个查询返回:

Date            qtySum      weightSum
----------------------------------------
2016-01-20      1           1
2016-01-21      2           2

完成此交叉连接后，您将结束:

Date            qtySum      a.weightSum     b.weightSum     barcodeCount
--------------------------------------------------------------------------
2016-01-20      1           1               26              8
2016-01-20      1           1               9               14
2016-01-20      1           1               4               7
2016-01-21      2           2               26              8
2016-01-21      2           2               9               14
2016-01-21      2           2               4               7

因此，A 中的每一行都与 B 中的每一行相匹配，总共有 6 行。

你的第三个问题是你然后按日期分组，但不执行任何聚合，没有深入研究 SQL 标准的细则、group by 子句和功能依赖性，让我们将其简化为 MySQL 允许这个，但你不应该这样做，除非你了解限制(这在 this answer 中有更详细的介绍)。 select 中不在 group by 子句中的任何内容都应该在聚合中。

因此，由于 MySQL 的 GROUP BY 扩展通过选择所有内容并仅按日期分组，您实际上是说每个日期取 1 行，但您无法控制哪一行，它可能是每个组的第一行如上所示，您将得到的结果是:

Date            qtySum      a.weightSum     b.weightSum     barcodeCount
--------------------------------------------------------------------------
2016-01-20      1           1               26              8
2016-01-21      2           2               26              8

我认为这就是为什么您最终会重复子查询 B 中的所有相同值。

这样就涵盖了错误所在，现在开始解决方案，假设 stock_list 中的日期在 selected_items 中不存在，反之亦然需要完全连接，但由于 MySQL 不支持此功能，因此您必须使用 UNION，最简单的方法是:

SELECT  t.Date,
        SUM(t.StockQuantity) AS StockQuantity, 
        SUM(t.StockWeight) AS StockWeight, 
        SUM(t.SelectedWeight) AS SelectedWeight, 
        SUM(t.BarcodeCount) AS BarcodeCount
FROM    (   SELECT  date, 
                    SUM(qty) AS StockQuantity, 
                    SUM(weight) AS StockWeight, 
                    0 AS SelectedWeight, 
                    0 AS BarcodeCount
            FROM    stock_list
            GROUP BY Date
            UNION ALL
            SELECT  date, 
                    0 AS StockQuantity, 
                    0 AS StockWeight, 
                    SUM(weight) AS SelectedWeight, 
                    COUNT(BarCode) AS BarcodeCount
            FROM    selected_items
            GROUP BY Date
        ) AS t
GROUP BY t.Date;

编辑

我无法对此进行测试，也不确定您的确切逻辑，但您可以使用 variables to calculate a running total in MySQL .这应该给出如何做的想法:

SELECT  Date,
        StockQuantity,
        StockWeight,
        SelectedWeight,
        BarcodeCount,
        (@w := @w + StockWeight -  SelectedWeight) AS TotalWeight,
        (@q := @q + StockQuantity - BarcodeCount) AS TotalQuantity
FROM    (   SELECT  t.Date,
                    SUM(t.StockQuantity) AS StockQuantity, 
                    SUM(t.StockWeight) AS StockWeight, 
                    SUM(t.SelectedWeight) AS SelectedWeight, 
                    SUM(t.BarcodeCount) AS BarcodeCount
            FROM    (   SELECT  date, 
                                SUM(qty) AS StockQuantity, 
                                SUM(weight) AS StockWeight, 
                                0 AS SelectedWeight, 
                                0 AS BarcodeCount
                        FROM    stock_list
                        GROUP BY Date
                        UNION ALL
                        SELECT  date, 
                                0 AS StockQuantity, 
                                0 AS StockWeight, 
                                SUM(weight) AS SelectedWeight, 
                                COUNT(BarCode) AS BarcodeCount
                        FROM    selected_items
                        GROUP BY Date
                    ) AS t
            GROUP BY t.Date
        ) AS t
        CROSS JOIN (SELECT @w := 0, @q := 0) AS v
GROUP BY t.Date;