按年龄、性别和 MySQL 中请求的报告分组数据

Question

我在制定 MySQL 语句/查询字符串时遇到问题。我有一张桌子（请参阅下面的示例）

这是一个包含性别、年龄和report_requested 字段的示例表。我想要的输出是这样的：

20 years old, male | Total number of users | Total who requested min 1 report | total who requested 2 reports | total 3 or more reports

20 years old female | Total number of users | Total who requested min 1 report | total who requested 2 reports | total 3 or more reports

20 years old combined | Total number of users | Total who requested min 1 report | total who requested 2 reports | total 3 or more reports

21 years old, male | Total number of users | Total who requested min 1 report | total who requested 2 reports | total 3 or more reports

21 years old female | Total number of users | Total who requested min 1 report | total who requested 2 reports | total 3 or more reports

21 years old combined | Total number of users | Total who requested min 1 report | total who requested 2 reports | total 3 or more reports

...等等

但我很难接受。我只知道根据性别和年龄确定请求（1,2,3,...等）信用报告的用户数量。

这是我使用的：

SELECT COUNT(*) as cnt, report_requested 
FROM sampletable WHERE age = '39' 
AND gender = 'M' GROUP BY report_requested

结果如下：

它只返回 20 岁男性的数据，请求 1 个信用报告的用户数量，2 个信用报告最多 8 个（但这也是错误的，因为它应该结合请求 3 个或更多信用报告的用户数量）

这里的任何人都可以帮助我或告诉我如何完成此任务吗？

Answer 1

您的GROUP BY 子句实际上是age 和gender，因为您正在尝试聚合这两个子句。考虑它的方式是，您希望每个 age 和 gender 正好有一行，即男性/20 岁 1 行，女性/20 岁 1 行，男性/21 岁 1 行，等等。所以你会这样做：

GROUP BY age, gender

而不是report_requested 列，我认为您需要SUM(report_requested) 并以请求的报告数量为条件。这是通过CASE 子句在SQL 中处理的。因此，您的查询将如下所示：

SELECT AGE, GENDER, 
    SUM(CASE WHEN report_requested = 1 THEN 1 ELSE 0 END) AS 'Total who requested 1 report',
    SUM(CASE WHEN report_requested = 2 THEN 1 ELSE 0 END) AS 'Total who requested 2 reports',
    SUM(CASE WHEN report_requested >= 3 THEN 1 ELSE 0 END) AS 'Total who requested 3 or more reports'
FROM sampletable 
GROUP BY AGE, GENDER

让我知道进展如何。我删除了WHERE 子句，因为我认为这只是为了测试。

编辑：在下面的 cmets 之后更新，这不是请求的总数，而是请求 1 份报告的总数，请求 2 份报告的总数等。