如何在SQL中添加變量

Question

我有一個變量，需要按月顯示。 此變量是布爾值，如果將其設置為True，則表示已安裝該應用程序。

示例：變量=已安裝的應用

一月有20個已安裝的應用程序。 2月有10個已安裝的應用程序。 3月，安裝了5個應用程序。

我想在桌上顯示所有已安裝的應用程序（布爾值= True）：

January: 20

February: 20 (January) + 10 =  30

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

有誰知道如何在Mysql中做到這一點？

謝謝

Answer 1

您可以使用子查詢按月對安裝進行分組。 然后，您可以在外部查詢中使用一個變量來計算累計和：

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

如果我理解正確，那只是一個帶有排序依據的簡單查詢。

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

希望您精通SQL，可以用所需的內容替換這些部分。

Answer 4

我假設您有一個“應用程序”表，其中包含“已安裝”列和“ InstalledDate”列。 如果是這樣的話...

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！ 我用了遞歸

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