SQL - 从两个不同的表中求和

Question

我试图在两个不同的表中总结两个不同属性中的值，但在执行此操作时遇到问题。所以我的表格结构是：

位置

• 位置ID (PK)
• 类型

员工要求

• 请求 ID (PK)
• positionID（来自位置的 FK）

招聘

• 招聘ID(PK)
• requestID（来自 StaffRequest 的 FK）

定期招聘

• recruitmentID(PK, FK from Recruitment)
• numberOfWeeks

RegRecruitWeeklyTime

• ID (PK)
• recruitmentID(FK from RegularRecruitment)
• 小时

因此，这 5 个表与我要执行的查询有关。 RegRecruitWeeklyTime 表将包含正式员工的所有每周时间，并将特定 recruitmentID 的小时数相加将得出招聘人员每周工作的总小时数。 numberOfWeeks 表会告诉你新兵应该工作的小时数。

现在我想编写一个查询，它将给出总小时数和总周数，并按职位类型对它们进行分组。这必须在单个查询中完成。

所以，起初我写了两个查询来执行每个求和。

SELECT
  Position.type AS 'Position',
  SUM(RegularRecuitment.numberOfWeeks) AS 'Total Weeks'
FROM Position, StaffRequest, Recruitment, RegularRecuitment
WHERE 
  Recruitment.recruitmentID = RegularRecuitment.recruitmentID 
  AND
  StaffRequest.requestID = Recruitment.requestID
  AND
  Position.positionID = StaffRequest.positionID
GROUP BY Position.type;

和

SELECT 
  Position.type AS 'Position',
  SUM(RegRecruitWeeklyTime.hours) AS 'Total hours'
FROM Position, StaffRequest, Recruitment, RegularRecuitment, RegRecruitWeeklyTime
WHERE
  RegRecruitWeeklyTime.recruitmentID = RegularRecuitment.recruitmentID
  AND
  Recruitment.recruitmentID = RegularRecuitment.recruitmentID 
  AND
  StaffRequest.requestID = Recruitment.requestID
  AND
  Position.positionID = StaffRequest.positionID
GROUP BY Position.type;

如果我分别运行这两个查询，它可以正常工作并给我正确的结果。但是，当我像这样组合这两个查询时：

SELECT 
  Position.type AS 'Position', 
  SUM(RegRecruitWeeklyTime.hours) AS 'Total hours each week',
  SUM(RegularRecuitment.numberOfWeeks) AS 'Total Weeks'
FROM Position, StaffRequest, Recruitment, RegRecruitWeeklyTime, RegularRecuitment
WHERE
  RegRecruitWeeklyTime.recruitmentID = RegularRecuitment.recruitmentID
  AND
  Recruitment.recruitmentID = RegularRecuitment.recruitmentID 
  AND
  StaffRequest.requestID = Recruitment.requestID
  AND
  Position.positionID = StaffRequest.positionID
GROUP BY Position.type;

'Total Weeks' 列乘以RegRecruitWeeklyTime 中的行数，表示结果为SUM(RegularRecuitment.numberOfWeeks) * COUNT(RegRecruitWeeklyTime.hours)。如果我将“总周数”列值除以 COUNT(RegRecruitWeeklyTime.hours)，我会得到正确的答案，但我只是想知道是否有更好的方法。

谢谢...

Answer 1

问题是找到'Total hours' RegRecruitWeeklyTime 表与RegularRecuitment 连接以获得结果，但找到'Total Weeks' 你没有加入RegRecruitWeeklyTime 表所以。当您尝试组合查询时，'total weeks' 显然会有所不同。试试这个..

SELECT A.Position,
       A.Total_Weeks,
       A.Total_hours
FROM   (SELECT Position.type                        AS 'Position',
               Sum(RegularRecuitment.numberOfWeeks) AS 'Total_Weeks'
        FROM   Position
               JOIN StaffRequest
                 ON Position.positionID = StaffRequest.positionID
               JOIN Recruitment
                 ON StaffRequest.requestID = Recruitment.requestID
               JOIN RegularRecuitment
                 ON Recruitment.recruitmentID = RegularRecuitment.recruitmentID
        GROUP  BY Position.type) a
       JOIN (SELECT Position.type                   AS 'Position',
                    Sum(RegRecruitWeeklyTime.hours) AS 'Total_hours'
             FROM   Position
                    JOIN StaffRequest
                      ON Position.positionID = StaffRequest.positionID
                    JOIN Recruitment
                      ON StaffRequest.requestID = Recruitment.requestID
                    JOIN RegularRecuitment
                      ON Recruitment.recruitmentID = RegularRecuitment.recruitmentID
                    JOIN RegRecruitWeeklyTime
                      ON RegRecruitWeeklyTime.recruitmentID = RegularRecuitment.recruitmentID
             GROUP  BY Position.type) b
         ON A.Position = B.Position 

Answer 2

你用的是什么数据库？？

如果你使用的是 sqlserver

你总是可以这样做

SELECT 
(
  SELECT
    Position.type AS 'Position',
    SUM(RegularRecuitment.numberOfWeeks) AS 'Total Weeks'
  FROM Position, StaffRequest, Recruitment, RegularRecuitment
  WHERE
    Recruitment.recruitmentID = RegularRecuitment.recruitmentID 
    AND
    StaffRequest.requestID = Recruitment.requestID
    AND
    Position.positionID = StaffRequest.positionID
  GROUP BY Position.type
) AS select1,

(
  SELECT
    Position.type AS 'Position',
    SUM(RegRecruitWeeklyTime.hours) AS 'Total hours'
  FROM Position, StaffRequest, Recruitment, RegularRecuitment, RegRecruitWeeklyTime
  WHERE
    RegRecruitWeeklyTime.recruitmentID=RegularRecuitment.recruitmentID
    AND
    Recruitment.recruitmentID = RegularRecuitment.recruitmentID 
    AND
    StaffRequest.requestID = Recruitment.requestID
    AND
    Position.positionID = StaffRequest.positionID
  GROUP BY Position.type
) AS select2