MySQL CASE语句，带有直方图的子查询

我正在尝试收集数据以创建直方图。我想创建用户登录系统次数的直方图。我的目标是利用answer中的函数，但如果有更好的方法，我也可以

我的登录表与此类似：

datetime | userid

我的第一步是获取用户登录的次数计数：

select count(userid) from logins group by userid

这将返回一个很好的结果集，类似于：

1325
761
4012
1204
662
1841
15
1698
...

我的问题是，我如何调整它以利用链接答案中的SELECT CASE WHEN方法。该代码如下所示：

SELECT CASE WHEN age BETWEEN 13 AND 17 THEN '13-17' 
            WHEN age BETWEEN 18 AND 25 THEN '18-25' 
            ELSE '26+' END AS AgeGroup,
    COUNT(*) AS total
FROM MyTable
GROUP BY AgeGroup

---

然而，在我的例子中，WHEN子句中的age是一个子查询，我认为不需要为每个WHEN运行它。利用这些箱子中的计数的有效方法是什么？

您需要通过以下方式将箱子添加到组中：

select case when age between 13
                and 17 then '13-17' when age between 18
                and 25 then '18-25' else '26+' end as AgeGroup,
    COUNT(*) as total
from MyTable
group by case when age between 13
                and 17 then '13-17' when age between 18
                and 25 then '18-25' else '26+' end

如果您想写一次案例，请执行以下操作：

select AgeGroup,
    count(*) as total
from (
    select case when age between 13
                    and 17 then '13-17' when age between 18
                    and 25 then '18-25' else '26+' end as AgeGroup
    from MyTable
    ) t
group by AgeGroup

---

因此，看起来您希望确定登录次数的范围，在这种情况下，您首先计算每个用户的登录尝试次数，然后将各个次数合并到不同的存储桶中

以下查询将提供登录1-2次、3-4次和4次以上的用户数

工作小提琴：

如果需要根据实际登录计数创建存储桶，请使用SUMtotal_登录而不是COUNTuser_id，如下查询：

SELECT CASE WHEN total_logins BETWEEN 1 AND 2 THEN '1-2' 
            WHEN total_logins BETWEEN 3 AND 4 THEN '3-4' 
            ELSE '4+' 
       END AS LoginGroup,
       SUM(total_logins) AS total
FROM (
  SELECT userid, COUNT(*) AS total_logins 
  FROM login 
  GROUP BY userid
) t
GROUP BY LoginGroup

---

请看一下这个代码

SELECT 
CASE age 
    WHEN BETWEEN 13 AND 17 THEN '13-17' 
    WHEN BETWEEN 18 AND 25 THEN '18-25' 
    ELSE '26+'
END AS AgeGroup,
COUNT(*) AS total
FROM MyTable
GROUP BY CASE age 
    WHEN BETWEEN 13 AND 17 THEN '13-17' 
    WHEN BETWEEN 18 AND 25 THEN '18-25' 
    ELSE '26+'
END

---

您希望结果如何？

SELECT 
CASE age 
    WHEN BETWEEN 13 AND 17 THEN '13-17' 
    WHEN BETWEEN 18 AND 25 THEN '18-25' 
    ELSE '26+'
END AS AgeGroup,
COUNT(*) AS total
FROM MyTable
GROUP BY CASE age 
    WHEN BETWEEN 13 AND 17 THEN '13-17' 
    WHEN BETWEEN 18 AND 25 THEN '18-25' 
    ELSE '26+'
END