MySQL将groupBy子句拆分为多列

Question

我对复杂的MySQL查询的知识不好，并且在搜索甚至措辞上都遇到问题。

我有一个表，如下所示。

我有一个查询，该查询计算“类型=学生”的所有行，然后按年份和月份将使用create_column的行进行分组。 这很简单。

查询看起来像这样：

SELECT YEAR(created_at) as year, MONTH(created_at) as month, COUNT(type) as student_count
FROM users
WHERE type = "student"
GROUP BY year, month
ORDER BY year, month

现在，我需要再添加2列“订阅”和“ pay_per_video”，这将把每个月和每年的总数进一步划分为学生级别类型的“订阅”或“ pay_per_video”。 例如。 如果在2017年1月共有20名学生注册。 每视频学生12名，而当月有8名是订阅学生。 任何指针，不胜感激。

更新我正在寻找的是这样的：表：Subject_Selection

Year    Month       Student Count     Pay Per View     Subscription
--------------------------------------------------------------------
2016     12              20                 20               0
2017     1               23                 12              11
2017     2               30                 10              20
2017     3                2                  1               1
2017     4               12                  2              10
2017     5               90                 40              50
2017     6               12                  0              12

Answer 1

使用如下条件聚合：

SELECT YEAR(created_at) as year, MONTH(created_at) as month, COUNT(type) as student_count,
count(case when student_level='subscription' then 1 end) as subscriptioncount,
count(case when student_level='pay_per_vedio' then 1 end) as pay_per_vediocount
FROM users
WHERE type = "student"
GROUP BY year, month
ORDER BY year, month

Answer 2

请在下面查询您的需要。 我希望它将按您的意愿执行。

SELECT YEAR(created_at) as year, MONTH(created_at) as month, student_level, 
COUNT(type) as student_count
FROM users
WHERE type = "student"
GROUP BY year, month, student_level
ORDER BY year, month, student_level

Answer 3

现在，我需要再添加2列“订阅”和“ pay_per_video”，这将把每个月和每年的总数进一步划分为学生级别类型的“订阅”或“ pay_per_video”。

在这里，我建议您仅添加一个名为level_type之类的列，该列将存储订阅或“ pay_per_video”作为值。

通过这样做，您的SQL将得到优化，

SELECT year, month, COUNT(student_count), level_type FROM (SELECT YEAR(created_at) as year, MONTH(created_at) as month, COUNT(type) as student_count
FROM users
WHERE type = "student"
GROUP BY year, month
ORDER BY year, month) as s
GROUP BY level_type