加入 CTE 按月/年分组

Question

我有多个 CTE，这会导致以下通用表结构：

Year | Month | Total_Purchases_Product_Line_X

这些代表按月和年分组的跨多个产品线的购买。

例如）

SELECT * FROM cte_line_x    

Year | Month | Total_Purchases_Product_Line_X
2018    01      256
2018    02      192

SELECT * FROM cte_line_y    

Year | Month | Total_Purchases_Product_Line_Y
2018    01      76
2018    02      59

我想创建类似下面的东西

Year | Month | Total_Purchases_Line_X | Total_Purchases_Line_Y | Total_Purchases_Line_Z
2018    01     256                       76
2018    02     192                       59

每个产品线的总采购量相加。但是，在将每个 CTE 的日期组合在一起后，我遇到了问题。 这是我尝试过的：

SELECT 
    cte_product_x.Month, 
    cte_product_x.Year, 
    cte_product_x.total as Total_X, 
    cte_product_y.total as Total_Y, 
    cte_product_z.total as Total_Z
FROM 
     cte_product_x
LEFT JOIN
     cte_product_y ON
     cte_product_y.year = cte_product_x.year
     AND
     cte_product_y.month = cte_product_x.month
LEFT JOIN
     cte_product_z ON
     cte_product_z.year = cte_product_x.year
     AND
     cte_product_z.month = cte_product_x.month
 GROUP BY 
    cte_product_x.Month, 
    cte_product_x.Year
  ORDER BY 
    cte_product_x.Month, 
    cte_product_x.Year

我尝试将我的 SELECT 更改为：

SELECT 
    cte_product_x.Month, 
    cte_product_x.Year, 
    MAX(cte_product_x.total as Total_X), 
    MAX(cte_product_y as Total_Y), 
    MAX(cte_product_z as Total_Z)

但是，它仅适用于“Total_X”。其他列的计数是为所有月份的分组总数找到的最大值。我不明白为什么。

Answer 1

这不行吗？

SELECT x.Month, x.Year, x.total as Total_X, 
       y.total as Total_Y, z.total as Total_Z
FROM cte_product_x x JOIN
     cte_product_y y
     ON y.year = x.year AND y.month = x.month JOIN
     cte_product_z z
     ON z.year = x.year AND z.month = x.month
ORDER BY x.Month, x.Year;

至少它适用于您的示例数据。