SQL Group By 以选择值的百分比

Question

我正在使用 Access（我知道 JET SQL 与 T-SQL 不同，但如果您在 T-SQL 中有答案，我会尝试翻译它）并且我有以下内容：

• 表 Department 以及部门名称和 ID 以及其他信息
• 包含应用程序列表以及它们是否可部署（布尔值/位）的表格应用程序
• 表 ApplicationMapping 链接 DepartmentId 和 ApplicationId（n:n 关系）

我试图了解每个部门有多少应用程序是可部署的（容易），但也有多少是不可部署的，以及完成的百分比。 （或至少类似于 (count(where deployable = true)/count(*))

我真的不知道如何进行这样的查询。 有什么想法吗？

Answer 1

（此答案是在 Access 2010 下开发和测试的。）

首先，我们需要一个查询，为您提供按部门划分的申请总数。简单：

SELECT DepartmentId, Count(*) AS CountOfApplications
FROM ApplicationMapping
GROUP BY DepartmentId

说给我们

DepartmentId  CountOfApplications
------------  -------------------
           1                    4
           2                    1

您已经有了按部门计算可部署应用程序的查询，可能看起来像这样

SELECT 
    am.DepartmentId, 
    Sum(IIf(a.Deployable,1,0)) AS CountOfDeployable
FROM
    ApplicationMapping AS am
    INNER JOIN
    Applications AS a
        ON am.ApplicationId = a.ApplicationId
GROUP BY DepartmentId

假设它给了我们

DepartmentId  CountOfDeployable
------------  -----------------
           1                  2
           2                  1

那么我们需要做的就是将这两个查询连接在一起

SELECT 
    q1.DepartmentId,
    q2.CountOfDeployable / q1.CountOfApplications AS pctDeployable
FROM
    (
        SELECT DepartmentId, Count(*) AS CountOfApplications
        FROM ApplicationMapping
        GROUP BY DepartmentId
    ) AS q1
    INNER JOIN
    (
        SELECT 
            am.DepartmentId, 
            Sum(IIf(a.Deployable,1,0)) AS CountOfDeployable
        FROM
            ApplicationMapping AS am
            INNER JOIN
            Applications AS a
                ON am.ApplicationId = a.ApplicationId
        GROUP BY DepartmentId
    ) AS q2
        ON q1.DepartmentId = q2.DepartmentId

我们得到

DepartmentId  pctDeployable
------------  -------------
           1            0.5
           2              1

编辑：

如果您想要一个包含所有部门的列表，即使是那些没有任何应用程序的部门，那么只需将整个前面的查询包装在另一个对 [Department] 表执行外部联接的查询中：

SELECT
    d.DepartmentId,
    d.DepartmentName,
    IIf(IsNull(calc.DepartmentId),0,calc.CountOfApplications) AS totalApplications,
    calc.pctDeployable
FROM
    Department AS d
    LEFT JOIN
    (
        SELECT 
            q1.DepartmentId,
            q1.CountOfApplications,
            q2.CountOfDeployable / q1.CountOfApplications AS pctDeployable
        FROM
            (
                SELECT DepartmentId, Count(*) AS CountOfApplications
                FROM ApplicationMapping
                GROUP BY DepartmentId
            ) AS q1
            INNER JOIN
            (
                SELECT 
                    am.DepartmentId, 
                    Sum(IIf(a.Deployable,1,0)) AS CountOfDeployable
                FROM
                    ApplicationMapping AS am
                    INNER JOIN
                    Applications AS a
                        ON am.ApplicationId = a.ApplicationId
                GROUP BY DepartmentId
            ) AS q2
                ON q1.DepartmentId = q2.DepartmentId
    ) AS calc
        ON d.DepartmentId = calc.DepartmentId

返回

DepartmentId  DepartmentName  totalApplications  pctDeployable
------------  --------------  -----------------  -------------
           1  Department1                     4            0.5
           2  Department2                     1              0
           3  Department3                     0               

Answer 2

在这种情况下你必须使用 join -

• 以下查询应该会给你想要的结果，但在 Oracle 数据库中。 我不知道如何翻译成 Access。

  SELECT department_id,
         total_cnt,
         (deployable_cnt / total_cnt) * 100 deployable_perc,
         100 - (deployable_cnt / total_cnt) * 100 not_deployable_perc
  FROM (SELECT dep.department_id,
               COUNT(*) total_cnt,
               SUM(CASE
                    WHEN app.deployable = 'Y' THEN
                    1
                    ELSE
                    0
                   END) deployable_cnt
         FROM department dep, applications app, applicationmapping appmap
        WHERE appmap.application_id = app.application_id
         and  appmap.department_id =  dep.department_id
   -- some other condition, if any
    GROUP BY dep.department_id)