mysql - 按天分组的累计总和

Question

我有这张表:

id
entry_date (timestamp)
exit_date (timestamp)

我需要显示每天的累计差异。实际上是平均值，但至少只是累积的。

所以输出将如下所示:

2015 1 1 33
2015 1 3 56
2015 2 4 77
2015 3 12 123

含义

Year month day cummulative_sum(exit_date-entry_date).

我检查过类似的线程:

MySQL cumulative sum grouped by date

Cumulative sum over a set of rows in mysql

Optimal query to fetch a cumulative sum in MySQL

Create a Cumulative Sum Column in MySQL

MYSQL request | GROUP BY DAY

但是这些解决方案都不适合我。我越来越渴望仅用 SQL 来完成此任务。 但这些任务听起来如此简单，以至于很难相信解决方案很难找到。

Answer 1

你也许可以做一些更有效率的事情，但我相信这是让你继续前进的东西。而且您的解释并不清晰，因此您可能需要提供一些示例数据来阐明您的需求。

select
    event_date,
    (
        select sum(+1) from T as t2 where cast(t2.entry_date as date) <= d.event_date +
        select sum(-1) from T as t3 where cast(t3.exit_date  as date) <= d.event_date
    ) as cumulative_total /* at end of day */
from (
    select cast(entry_date as date) as event_date from T union all
    select cast(exit_date  as date) from T
) as d
group by event_date

将 T 替换为您的表的名称。我还使用了强制转换来消除时间，但我不确定这在 MySQL 中是否真的有效。

平均天数(不包括任何未由进入或退出表示的日期)也很容易:

select avg(cumulative_total) as average_per_day
from (
    select
        (
            select sum(+1) from T as t2 where cast(t2.entry_date as date) <= d.event_date +
            select sum(-1) from T as t3 where cast(t3.exit_date  as date) <= d.event_date
        ) as cumulative_total /* at end of day */
    from (
        select cast(entry_date as date) as event_date from T union all
        select cast(exit_date  as date) from T
    ) as d
    group by event_date
) as d2