Question

我想跟踪不同部门在工作中进行的调查。通过使用“分组依据”并计算匹配数量，这很容易做到。

SELECT     Departments.DepartmentName, count(*) as [survey count]
FROM         Departments INNER JOIN
                  Surveys ON Departments.DepartmentID =  Surveys.DepartmentID
 GROUP BY Departments.DepartmentName

但这仅显示已完成调查的部门。如何将未完成调查结果列表的部门作为零计数？

更新

SELECT     Departments.DepartmentName AS Department, 
        COUNT( Surveys.DepartmentID) AS      [survey count]
        , Departments.DepartmentID
        FROM          Surveys FULL OUTER JOIN
                  Departments ON  Surveys.DepartmentID = Departments.DepartmentID
   GROUP BY Departments.DepartmentName, Departments.DepartmentID

Answer 1

您需要一个“左外连接”而不是“内连接” - 这将在输出中生成行，其中所有与“survey”对应的列为null，其中没有匹配连接条件。

您需要将查询更新为“count（Surveys.DepartmentID）”或“sum（survey.departmentID不为null，然后是1，否则为0）”，以避免将这些行计为单个提交。< / p>

Answer 2

将INNER JOIN替换为LEFT JOIN。即使没有相关的调查，它也会选择所有部门。

Answer 3

只需将INNER JOIN更改为LEFT JOIN并将COUNT（）更改为仅引用SURVEYS。那可能就像那时一样。

SELECT     Departments.DepartmentName,
           count(Surveys.DepartmentID) as [survey count]
FROM         Departments LEFT JOIN
              Surveys ON Departments.DepartmentID =  Surveys.DepartmentID
 GROUP BY Departments.DepartmentName

Answer 4

SELECT Departments.DepartmentName, count(Surveys.DepartmentID) as [survey count]
FROM Departments
LEFT OUTER JOIN Surveys
ON Departments.DepartmentID =  Surveys.DepartmentID
GROUP BY Departments.DepartmentName

Answer 5

SELECT     Departments.DepartmentName, count(Surveys.*) as [survey count]
FROM       Departments 
LEFT JOIN  Surveys ON Departments.DepartmentID =  Surveys.DepartmentID
GROUP BY   Departments.DepartmentName

请注意 LEFT 加入和计数的变化（调查。*）

在sql中计算匹配

5 个答案: