mysql - 去年 7 月到 7 月之间哪些 CD 的销量更高

Question

销售，因为一个日期可以有很多销售，并且会有很多行。

但是我不确定我该怎么做。

到目前为止，我有：

SELECT cd_no
FROM sales

我认为是在子查询选择中，别名“m”返回“NULL”

Answer 1

您可以通过按 CD_NO 分组并计算行数来计算每张 CD 的总销售额：

SELECT CD_NO, COUNT(*) AS purchases
FROM Sales
GROUP BY CD_NO

您可以像这样获取特定日期范围内每张 CD 的销售数量（因为<date condition>True 时为 1，False 时为 0）：

SELECT CD_NO, SUM(<date condition>) AS purchases
FROM Sales
GROUP BY CD_NO

对于 2012 年 7 月，您可以使用purchasedate BETWEEN '2012-07-01' AND '2012-07-31'或YEAR(purchasedate) = 2012 AND MONTH(purchasedate) = 7等选项。

比较两个日期范围

SELECT
    CD_NO,
    SUM(purchasedate BETWEEN '2012-07-01' AND '2012-07-31') AS a,
    SUM(purchasedate BETWEEN '2011-07-01' AND '2011-07-31') AS b
FROM Sales
GROUP BY CD_NO

最后，选择购买量增加 15% 的行...

SELECT CD_NO
FROM (
    SELECT
        CD_NO,
        SUM(purchasedate BETWEEN '2012-07-01' AND '2012-07-31') AS a,
        SUM(purchasedate BETWEEN '2011-07-01' AND '2011-07-31') AS b
    FROM Sales
    GROUP BY CD_NO) AS t
WHERE t.a > 1.15 * t.b

或者简单地说：

SELECT CD_NO
FROM Sales
GROUP BY CD_NO
HAVING       SUM(purchasedate BETWEEN '2012-07-01' AND '2012-07-31') 
     > 1.15 * SUM(purchasedate BETWEEN '2011-07-01' AND '2011-07-31') ;