如何对表中的值进行分组并从2个不同的表中获取2个不同的列之间的差异

Question

我要额外增加两个表，并保存所有表，它们有一个列销售

    Table  extra                           Table  save      
   ITEMS  SALES                           ITEMS  SALES           
     A     15                                A     7                     
     B     20                                B     2                           
     A     2                                 A     5 
     B     2                                 B     2 

我想先按项目对元素进行分组，然后从表保存中的销售列减去表中的销售列，然后将结果放入带有列的另一个订单表中（项目差异），结果应如下所示

   Table  order                                
   ITEMS  difference                                    
     A     5                                                  
     B     18                                                       

Answer 1

尝试这个：

SELECT T1.ITEMS,T1.extraSales-T2.saveSales as Difference FROM 
(SELECT ITEMS,SUM(SALES) as extraSales FROM extra GROUP BY ITEMS) T1
INNER JOIN 
(SELECT ITEMS,SUM(SALES) as saveSales FROM save GROUP BY ITEMS) T2
ON T1.ITEMS=T2.ITEMS

结果：

ITEMS   DIFFERENCE
A       5
B       18

编辑：

要将其插入到另一个表中：

INSERT INTO orderTable VALUES
(
SELECT T1.ITEMS,T1.extraSales-T2.saveSales as Difference FROM 
(SELECT ITEMS,SUM(SALES) as extraSales FROM extra GROUP BY ITEMS) T1
INNER JOIN 
(SELECT ITEMS,SUM(SALES) as saveSales FROM save GROUP BY ITEMS) T2
ON T1.ITEMS=T2.ITEMS
)