如何在SQL中添加变量

Question

我有一个变量，需要按月显示。 此变量是布尔值，如果将其设置为True，则表示已安装该应用程序。

示例：变量=已安装的应用

一月有20个已安装的应用程序。 2月有10个已安装的应用程序。 3月，安装了5个应用程序。

我想在桌上显示所有已安装的应用程序（布尔值= True）：

January: 20

February: 20 (January) + 10 =  30

March: 20 (January) + 10 (February) + 5 (March) = 35

有谁知道如何在Mysql中做到这一点？

谢谢

Answer 1

您可以使用子查询按月对安装进行分组。 然后，您可以在外部查询中使用一个变量来计算累计和：

select  installation_year
,       installation_month
,       installation_count
,       (@running_sum:= @running_sum + installation_count) as cumulative_sum
from    (
        select  year(installation_date) as installation_year
        ,       month(installation_date) as installation_month
        ,       count(*) as installation_count
        from    YourTable
        group by
                installation_year
        ,       installation_month
        ) as SubQueryAlias
join    (select @running_sum := 0) as InitVars
order by 
        installation_year
,       installation_month

SQL Fiddle中的示例。

Answer 2

就像是：

Select COUNT(*),Month 
From Apps
where installed = true
group by Month

Answer 3

如果我理解正确，那只是一个带有排序依据的简单查询。

select COLUMNS_YOU_WANT from TABLE_NAME 
where YOUR_BOOLEAN == True 
order by SOME_DATE_COLUMN

希望您精通SQL，可以用所需的内容替换这些部分。

Answer 4

我假设您有一个“应用程序”表，其中包含“已安装”列和“ InstalledDate”列。 如果是这样的话...

SELECT Count(*)
FROM   Applications
WHERE  Installed = 1 -- Assumes a bit/boolean column.
AND    InstalledDate BETWEEN @StartDate AND @EndDate;

史考特

Answer 5

我知道了！ 我用了递归

SELECT (select id_time from database.dim_time where id_time = a.fk_time) AS yearmonth, (select sum( if( installed in (1), 1,0)) as installed from database.facts_table where fk_time <= yearmonth ) as installed FROM database.facts_table AS a GROUP BY yearmonth ORDER BY yearmonth ASC