在不使用mysql连接的情况下合并两个表？

Question

我已经做了一次不合算的尝试来合并来自两个不同表格的值。第一个显示就像我想的那样，但第二个显示的只是第一行。

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。

这些是我selected_items表。

这是我的stock_list。

我的两个单独的查询工作，我得到了正确的输出只有当我试图运行它们放在一起就给出了第二query.Can任何一个问题指出我的错误或告诉我一个更好的方式来做到这一点。 这就是我的最终目标是

Answer 1

第一个问题是，你按日期在你的子查询B分组，但你不选择它，所以你的结果集可能是这样的：

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

这是结果3个日期，但你不知道哪一行是指哪个日期。

你的下一个问题是，您使用的是交叉连接，这是因为你的两个查询之间没有联系，这意味着如果你的第一个查询返回：

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

你做了之后这个交叉连接你结束

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 

所以A的每一行都与B的每一行相匹配，给你6个总行。

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，group by子句和函数依赖关系的细节，让它简化为MySQL允许这样做，但除非你明白限制（这在this answer的更详细的介绍中），否则你不应该这样做。 select中不在group by子句中的任何内容可能应该在聚合中。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，所以您实际上说的是每个日期取1行，但您无法控制哪一行，它可能是每行的第一行如上面显示的，所以你会得到的结果是组：

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

我想这是为什么你从子查询B中的所有相同的价值观结束了重复。

因此，这涵盖了什么是错误的，现在解决方案，假设stock_list中的日期在selected_items中不存在，反之亦然，您将需要一个完整的连接，但是因为这在MySQL中不受支持你将不得不使用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

我不能对此进行测试，我也不是确保您的确切逻辑的，但你可以使用variables to calculate a running total in MySQL。这应该给如何做的想法：

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; 

Answer 2

您可以使用join。但是，如果两个表中的日期集合不同，那么您需要full outer join。但是这在MySQL中不可用。相反：

select date, sum(qtySum), sum(weightsum1), sum(weightsum2), sum(barcodeCount) 
from ((Select date as Date, Sum(qty) as qtySum, Sum(weight) as weightSum1, 
       NULL as weightsum2, NULL as barcodeCount 
     From stock_list 
     Group by date 
     ) union all 
     (Select date, null, null, Sum(weight), Count(barcode) as barcodeCount 
     From selected_items 
     Group by date 
     ) 
    ) t 
Group by date; 

我不知道你想要的输出如何对应于您所提供的查询。但是，这应该按日期汇总和合并两个表中的数据，以便最终确定查询。

Answer 3

如果两个表中都不存在某些日期，则可以使用FULL JOIN运算符来解决您的任务。

Select ISNULL(A.date, B.date) AS date, 
     A.qtySum, 
     A.weightSum, 
     B.weightSum, 
     B.barcodeCount 
From 
    (Select date as Date, 
      Sum(qty) as qtySum, 
      Sum(weight) as weightSum 
    From stock_list 
    Group by date) as A 
FULL JOIN 
(Select date, 
     Sum(weight) as weightSum, 
     Count(barcode) as barcodeCount 
From selected_items 
Group by date) as B ON A.date = B.date